I was working as a game programmer and technical designer on a big budget FPS back when the original Half-Life was released, and immediately "AI AI AI!!!!!" became a stifling buzzword and thought-terminating (ironically) slogan, heavily reorienting how people thought about shooter design and, essentially, ending boomer shooters as a thing for a good long while and ushering in the era of Halo, Call of Duty, cover-based shooters, and so on.
I happened to adore boomer shooters and have good taste for their rhythms and making them, so the transition is not one I personally enjoyed at all.
But worse in a way, Half-Life ALSO ushered in much more linearity in level design because of their awesome interactive set pieces and the particular interactive way they got across their story. Certainly that was the way its release was experienced in the studio I was in, anyway. Less sprawling, unfolding, and backtracking like in Doom (where the space unfolds over the course of a level in something like a fractal way), more following a string of pearls and hitting all the scripted events, like a haunted house ride. You didn't want the players getting lost, you didn't want them to get bored backtracking, and you didn't want them to miss any of the cool one-off scripted content you'd made for them.
(I love Half-Life, so I don't blame it for any of this - it's a vastly more interesting game than many of the games it inspired, which I think is typical of highly innovative games)
At the time, I wasn't quite yet a thoughtful enough, perceptive enough game designer to recognize how deeply in tension those two changes ended up being with each other. And so I spent a miserable year of eventual burnout trying to make "good enemy AI that players actively notice" as a programmer for a game whose levels kept getting progressively tighter, more linear, and more constrained to support the haunted house ride of scripted events.
As a point of contrast, games like Thief and Thief 2 were magnificently structured for good, cool AI that players could notice, and it was specifically because of the non-linear ways the levels were built, the slow speed of the game, the focus on overtly drawing attention to both player and enemy sense information, and the relationship between the amount of space available to players at any given point to the amount of enemies they faced, as well as the often longer length of time players engaged with any particular set of enemies... and of course, despite all these cool features, poor, poor Thief was released to store shelves just 11 or 12 days after the original Half-Life. Business advice 101 is don't release your first person game 11 or 12 days after Half-Life.
Anyway, that all leads in to my admiration for Far Cry's design. Their outdoor levels actually steered their game design in a direction that could let enemy AI breathe and be an interesting feature of their design, in turn giving players higher level choices about when, where, and how to make initiate fights. In that sense, it reminded me of where Thief had already gone previously, but in the context of a high profile shooter. But doing that required actively relinquishing the control of the haunted house ride-style of pacing, which I think was kind of brave at the time.