Real world espionage takes many forms, but it mostly involves two aspects: intelligence and field operations. Intelligence is gathering data from a variety of methods and sources, from computer hacking to pillow talk. This data is then funneled to analysts and operations chiefs who decide what it means and what, if anything, to do with it. Field operations are sometimes conducted to gain intelligence (or protect intelligence assets) and other times to further other goals of the state, intelligence agency or other relevant party. For example, various agents of the Central Intelligence Agency distribute drugs, firearms and money by a variety of means to advance certain political and economic agendas in target nations and organizations. Though field operations will sometimes involve violence and the occasional car chase these are usually considered bungled missions. If the goal was actually to kill a lot of people espionage agents are not the choice method - mercenaries and WetWorks (essentially black ops military teams charged with illegal murders and kidnapping) are the weapon of choice. There is interplay between intelligence agencies and WetWorks, but they are not synonymous. The CIA does not have a military branch, though it may make use of military and paramilitary forces these forces are not actually part of the CIA.
A lot of intelligence work is considered boring, but this may be as much a case of their employers as the nature of intelligence work in general: modern states are bureaucracies, bureaucracies exist primarily to invent 'work' which justifies the spending of their budget - the employment of bureaucrats and the expansion of these bureaucrats' power is the overriding economic logic of the entirety of state organizations (including the military), and whatever mission objectives they put forth (even if they believe it themselves) is necessarily subordinate to the economic reality of bureaucracies. Bureaucracies that do not operate as employment scams and lobbying firms will cease to be politically competitive and will therefor cease to exist, or at least lose most of their money and power.
I suspect bureaucratic incentives and inertia is the primary reason that the NSA spends most of its time collecting huge amounts of random information, most of which is definitely useless and which exists in far too great a volume to possibly be usefully analyzed. Necessarily, most people at the NSA will be doing useless data collection and useless analysis on useless information. They will also have an incentive to invent fake utility and fake threats for this useless information and useless work, as they can not admit it is useless and thereby stop doing it - that would destroy the source of their jobs and the justification for their extraordinary power (including the personal power of many bureaucrats at the NSA, who have both extralegal means to push their agenda and the ability to influence lots of people and political actors through their ability to dispense money through jobs and contracts).
An intelligence agency that was operating under other incentives - such as actually solving mysteries and gaining useful intelligence, and not simply padding its nest and rationalizing its enormous staff - would operate in far different ways. While some of the technical aspects might be the same their targeting would be far more focused and far less wasteful, and they would likely ignore large swaths of pencil-pushing and build far fewer $80 million boondoggles to reward their friends at Boeing.
A private or non-bureaucratic intelligence agency would likely have more in common with the Pinkertons than the CIA - focused, non-arbitrary intelligence work is essentially detective work combined with organizational infiltration. The data analysts would likely be more like the people who work for Google than the people who work for the CIA - they have a set objective, a limited budget, a performance-based employment and have neither the need, nor staff, to simply photocopy the text messages of everyone in the world. Like advertisers, they want to make sure they are spying on and working over the right people.
In the adventure I am working on for GURPS the players will work for a private consortium which acts as an intelligence and security service for a variety of customers. This consortium has political-economic agendas of its own (as well as straightforward profit motives), and their customers likewise have certain ideological and economic agendas they wish to advance. But as they are fundamentally different in structure from traditional bureaucratic nation-states they differ radically in their scope and political incentives. They may try to overthrow foreign governments, but will not simply adopt regime change as a policy to rationalize spending billions in black budgets on foreign colonels, as in an intelligence bureaucracy. Instead they will first develop the objective to overthrow a certain state and then begin looking for ways to do it with the minimum possible cost and exposure. This will likely not be hiring 20,000 employees and constructing an enormous office building. The focus here is not on whether they are more or less benevolent than the KGB, but that the KGB was a state department whose continued budget and powers were the first priority to which any objective of communist revolution or finding traitors was subordinate - if no traitors existed, they would be found; and if revolution was hopeless that did not mean money could not still be spent on trying anyway.
Likewise the players can not act with the same arbitrary ruthlessness of the American and Soviet empire's intelligence agencies. They do not have the same level of integration into the ruling class and MIC elite, they do not have arbitrary police powers within the jurisdiction of their clients, etc. This is not to say that a private organization can not aspire to achieve a political hegemonic status and thereby gain such arbitrary powers and political protections (this is how most States are formed, often by barbarians) but so long as they have no actually become a political state they simply can not afford to act in such a manner even if they would like to. Without the power to tax one must actually earn a living.
A Short Rant on 'Boring' Games and Boring PeopleIt is often alleged that realistic spy games do not exist because real-world intelligence is boring. Yet much of the banality and inanity of real-world intelligence comes from the bureaucratic nature of it (likewise, real-world military service is typically boring and often varies between extreme tedium and trivially easy work), but I often hear this in regard to any genre - anything realistic is 'boring' because people play games to 'escape real life'. I can't speak to everyone's motives, but I usually play games to become engaged in a simulacrum of an interesting situation and/or play a game whose mechanics themselves produce novel and entertaining results. The huge numbers of people who actually enjoy realistic, logically consistent games shows that such claims are essentially a projection by people whose imaginative and intellectual capacities have likely been stunted by watching too many movies. Lots of people think history, economics, political theory, ancient warfare and basically anything that isn't explosions and tits is 'boring'. I call these people morons.
Some people find may find themselves mentally exhausted and wanting to 'zone out' after work, etc. even if they are not necessarily imbeciles. That, however, is not something I have ever experienced. I usually find movies boring because they do not engage my mind and make no sense, thus becoming a pointless spectacle to which I am simply insensate. I pretty much never 'wind down', I like to be doing something all the time. I would much rather read a biography of Hannibal or play a game of Command & Colors than watch most films or television shows. Anything which does not both enrich and engage my intellectual capacities is usually boring. I simply do not possess the capacity to stop thinking about things, nor would I ever want to. This makes me very hard to entertain - I have extremely high and rather specific 'standards' when it comes to what I want, though I do read dimestore trash novels such as Star Trek or The Executioner. What they have, though, is exploration of some aspect of ideology, psychology, mythology, etc. which I find engaging and underserved in other media. I like Superman because I enjoy sun gods and hysterically unbalanced playing fields, which is why I find attempts to 'humanize' Superman tedious. Superman is not a man - he is a superman.
Now while one might opt to 'live and let live' the reality is that I have to live in a world dominated by people whose tastes and habits I find tedious and atrocious, and whose huge numbers mean that they have a large influence on the market production and the overall shape of culture. The quintessential normies who take no enjoyment (probably because they lack the comprehension, for one thing) from classical history are not constantly confronted with television shows demonstrating a highly realistic depiction of the Roman Civil War. However, almost every television show ever made is aimed at their shitty taste. Likewise, one can easily avoid playing GURPS and find hundreds of games aimed at railroading, Snowflakism, simple rules and mindless combat. But I can not post something in an RPG forum without one of these idiots giving me the 10,000th version of the same tedious 'realizm iz boring' tirade, which all of these fuckwits apparently believe I have never heard before - they're so stupid they think their throw-away responses are actually informative to someone who obviously reads and plays games, and who obviously has a taste for whatever it is I am discussing or promoting. Being dumb is one thing, but one of the most striking features of the idiot normie is that he does not realize how predictable, tedious and completely obvious everything he says will be.
This has often been my response to psychiatric hacks - the idea that someone should be 'well adjusted' to a society of superstitious tyranny and dominated by packs of half-wits is risible. Anyone who finds themselves comfortable and accepting of such an environment is basically eugenics bait, and I don't care if that includes 98% of the planet. And I can't help but notice both a specific and thematic overlap between people who are able to 'turn off' their critical filters and 'just enjoy' a movie with people who do not question the norms and beliefs of their society at large, and indeed can not help but notice that this is not something they do themselves but also seem to be offended whenever someone refuses to do so. "Don't start asking questions, you'll make me think!" For some people, ignorance is bliss.
A final note is that while I do enjoy 'realism', because reality is the only consistent and fully implemented setting ever conceived, I am just as much interested in coherence and consistency in general. I would not mind madcap, absurd premises so much if people didn't stubbornly refuse to follow through on them. What's even worse are all the people making excuses for lazy, shitty writing because 'muhPlot'. I would much rather have a plot avoided or a setting changed to fit it, than to have a plot wedged into a setting it does not make sense in. The aforementioned people seem to think viewers have some social contract to passively accept the incompetence and ignorance of writers. But plenty of writers do put effort into realizing plots and trying to make the fantastic bits fit together. Most writers don't, and that's because they're bad writers.