3 is pretty easy but immersive. The immersion is mostly scripted though. 2 I never finished, which isn't weird I think. It's huge and, well, hardcore I suppose. The epicness is perhaps more rare but it's not scripted. All the epic things in Far Cry 3 are just coded, while in Far Cry 2 it's because you just happen to get yourself into shitty situation, because you can plan as much as you want, but if your weapon happens to jam the wrong second, things can get pretty crazy as everyone chases you... In Far Cry 3, your weapon never jams and you can just rambo your way out of everything. The immersiveness is good in Far Cry 3, but it's more of an illusion since you'll survive everything anyway, while in Far Cry 2 you will go down at some point, with potential buddies saving you, but you go down. Far Cry 3 is much less realistic. While the story line sounds so difficult to actually pull off, you don't have to worry since the game kinda pulls you through anyway. Far Cry 2 has hard stuff, but realistically hard stuff, and it actually is hard.
Far Cry 3 for a fun casual game that looks immersive. Far Cry 2 as an awesome time sink, and a potential for some of the epic moments that you will only experience in Far Cry 2.
It's hard to spend many hours on Far Cry 3 since the game is finished at some point and if you replay it, it really feels like you're doing the same things again. The epicness is much less epic to me at least when you've already seen all those scripted events before.
Far Cry 2 is hard to play through and I imagine that if you decided to play through it again, you would still get truly new experiences.