I was extremely impressed with the partner AI. I didn't have a single issue with the partner getting stuck anywhere or getting in the way. In fact, my partner often moved to the right spot for the puzzles before I even realized what needed to be done. And my partner would always revive me quite quickly the few times I died. So I'd say the game is immensely playable SP with the partner AI, in fact, it's well above average partner AI.
Likewise, playing SP is a great introduction to Hunted. Then you can replay it on the unlocked harder modes, either SP or Co-op. It's the type of game you can go back and replay every so often because it's just a lot of fun and has great pacing...too bad it's so under-appreciated. If you want a great dungeon exploration experience with fun combat, definitely buy it when it goes on sale for a good price.