One very common sentiment I see from old-time "hardcore" gamers (especially PC gamers) is that the vast majority of modern first-person shooter games are "dumbed down" compared to the greats of the 90's (ie. Doom, Quake and the other popular ones back then).
While I can appreciate what they feel, I really can't agree on the sentiment. In fact, I can actually present an argument for the exact opposite position.
Doom and Quake were essentially nothing more than shooting galleries. No story, no characters, no interaction with NPC's. It was simply one abstract level after another, levels with no storywise design or consistency (eg. trying to depict an actual location, like an actual spacestation or a factory), and your only mission was to kill enemies, push buttons and find the exit. That's it. There was absolutely nothing more to either game (nor to myriads of other similar games that are highly regarded by these people).
How much more "dumbed down" can you get than that? (Perhaps the only way would be to reduce the number of weapons and types of enemies.)
Compare that to modern first-person shooters. They have very elaborate stories, and very elaborate levels. Level design is invariably a lot more concrete and supports the narrative. While admittedly even today most FPS games consist of killing enemies, pressing buttons and finding the exit, most of them do present additional tasks as well. (In other words, while with some games you could argue that what you need to do is the exact same thing as with Doom or Quake, you can't argue that modern games are "dumbed down" based on that. At most they would be as "dumb" as Doom or Quake were.)
(Curiously, early alpha versions of Doom had levels that were less abstract, with actual recognizable locations like locker rooms, more clearly the insides of a spacestation, etc. These very early test levels also had fellow marines that would accompany you, and it was clearly planned to have an actual story of some kind. For some reason, however, in the final published version all the levels are highly abstract, with no real recognizable features, the real-object textures (such as locker doors) were replaced with more abstract textures, and the story was pretty much excised from the game. It was, dare I say, "dumbed down" quite a lot compared to those alpha versions.)
Many of these people talk about modern FPS games being "easier" than Doom or Quake. But are they? They seem to forget that both games had different difficulty settings, and they were quite trivially easy on the lowest settings. They also seem to ignore that a good portion of modern FPS games also have difficulty settings, and can be really hard on the highest settings, just like Doom and Quake were.
What I believe is happening here is that they found Doom and Quake to be really hard when they were young and inexperienced with FPS games, but nowadays they find FPS games relatively easy because they have decades of experience with them. They are comparing the experiences in their youth, when they didn't know how to play all that well, to their experiences today, when they have mastered the art of FPS gameplay. I think that they are not realizing this.
Another aspect of this is that modern games tend to implement lots of anti-frustration measures and tutorials that these old-time hardcore gamers find patronizing. I think this is a bit silly of a thing to complain about, because you can safely just ignore those things. (Also, many times the anti-frustration measures make playing a lot more enjoyable, by their very nature. Why would anybody want to play video games that are frustrating and unenjoyable?)
Then there's of course the question of linearity. Can the average modern FPS game be considered "dumbed down" because it's more linear than Doom or Quake were? Well, it depends on your perspective.
Doom and Quake were actually not as non-linear as people seem to want to think. Sure, each level was rather non-linear, often being quite open and requiring you to traverse to different parts of it to press those buttons and acquire those keys. However, the levels were relatively small in size, and the progress from level to level was purely and absolutely linear. At no point would you go back to a previous level to do anything. You passed one level, and that's it; you go to the next level and never come back. That is, in fact, quite linear gameplay (even though within the level the gameplay might not be as linear). When you think about it, it wasn't actually all that different from the average modern FPS game.
(And there are, of course, plenty of pretty non-linear FPS games out there. Those with a great deal of exploration to them, and where you can go back to any level you have already been in, and sometimes even have to go back for something. Alien: Isolation comes immediately to mind as a perfect example.)
When a game is too linear, it can be a bit bothersome. However, linearity allows for stronger storytelling, and when that part is well done, the linearity is not such a big deal. Sometimes a video game, even a first-person shooter, is a storytelling experience, and that's ok. Is such a game "dumbed down" compared to Doom and Quake (which had no story whatsoever)? Your mileage may vary.
Many modern FPS games, on the other hand, contain technological and game design innovations that FPS games of the 90's did not have. Stealth-based gameplay is a perfect example. Physics engines are another (especially when those engines are used for actual gameplay). Enemy AI has improved drastically compared to Doom and Quake (with enemy squads using tactics like flanking and taking cover, flushing you out with grenades, etc.) This is the exact opposite of "dumbing down".
In my opinion modern FPS games are not "dumbed down" compared to Doom, Quake or any of the other great 90's FPS games. In fact, I'm of the opposite opinion.