www.aigamedev.com has all the skinny on the current work happening on videogame AI.
Long story short: There’s a ton of techniques, some of which work and some of which require more thinking. Machine learning was a big thing a few years ago and there was a lot of discussion about its applicability, but for the most part AI for shooter type games still uses what we call reactive planners. I.E behavior tree’s and their ilk.
You can do simple “learning” fairly easily, but its an ongoing area of AI research so you can go as far as you like really (plenty of PhD level work to do still in that area).
If you’re interested, there are a loads of competitions for game AI being run. One of them was an Unreal Bot competition. So maybe google the results of that.