Lets just get to the best bits right away. Ok, so I've never played Half-Life, but JA2 beats the rest in sheer fun, combatwise. It even makes the x-coms pale by comparison
I think there are two types of fun combat, the one where you need to commit all your grey cells to win and the one where you need all your adrenaline glands to win. Stalker would fall in the latter category for me. I found combat quite challenging (almost frustratingly difficult at times).
Bloodlines combat was nice. Not bad, but not really either/or either, or?... Combat was functional. It was there, served a purpose, but it wasn't the reason you played/enjoyed the game.
I have to play ToEE too some day. It's been gathering dust ever since I picked it up from a bargain bin.