Three.js is like a javascript toolkit. You can load blender models, including enemy characters and you can animate them. But you will have to create the basic javascript program yourself, including things like enemy ai. And, in fact, that is how things should be if you plan to create something unique that is worth playing and not just a copy of what someone else has done.
I think you are looking in the right place. I have found that YouTube has a lot of useful tutorials discussing how to create simple games using javascript, blender and three.js. One resource that I have found useful is SimonDev. He has a few tutorials showing how to create a flying game. If you want something ground-based, you might check out Bláha. He created a three.js driving/flying simulation and posted the entire source code. It is several years old - but is so entertaining that several people are currently trying to update and improve on it. You can find discussions about this simulation on this site. Here is another example on this site.