Can you help me decide?

Dude, it's assassin's Creed. You've played AC2, you've played them all. So yeah, go for it.
But think of the fact that you'd have to download uPlay and you'd be supporting the company that said "90% of PC gamers pirate games."

I personally enjoyed Torchlight II, gave it ~150 hours and still intend to continue later with my character.

Probably it's because I give gameplay/replayability much more priority rather than story based games, and personally if I was interested in story, I would watch walkthrough/game movie with all cutscenes in youtube.

Kingdoms of Amalur. It took me about 100hours to finish the game. Story is very surprising especially the ending but the game is too easy even on hardest difficulty if you do side quests. Consider R.A. Salvatore and Todd McFarlane before buying :P Also gameplay is really satisfying.
Other games are good too but I'd choose KoA.

Torchlight is super fun :3

I really enjoyed Black Flag (actually, I really enjoyed most AC games), so voted for that one. AC2 is great as well, but in my opinion Black Flag was a bit more fun.

The one I haven't played is Black Flag so can't say anything about that.

I would go with Kingdoms of Amalur, as that was the one I found the most engaging. While AC2 and Torchlight 2 became boring somehow. (I really wanted to like Torchlight 2 but it never happened :( )

I think you can't really go wrong with any of these games, you get solid play time out of everyone of these, so I'd say you should buy the genre you would enjoy the most.

Black Flag is a really nice game and it's a lot different than the other Assassin's Creed games. So, go for it. ;P

Assassin's Creed games are overrated. Also Uplay...

Torchlight 2 has really bad story. Alchemist goes on a rampage, goes after guardians to take their power. You get to one guardian he tells you Alchemist was already here and sends you to the next. When you get to the next he tells you Alchemist was already here and sends you to the next and so on. Like seriously it's lame as hell. Side-quests for the most part also aren't interesting or fun. I can tolerate bad story and side-quests if game has incredible gameplay but unfortunately Torchlight 2 does not. I enjoyed the first Torchlight and the old Fate game more.

Kingdoms of Amalur has an interesting story and side quests. Skill animations if I remember right are awesome and combat is enjoyable. It's been so long since I played this game but if I remember right the only negative thing about it for me was the difficulty or should I say the lack thereof. The game is easy even on the hardest difficulty which eventually got me bored and I never finished it. I'll probably pick it up on steam some day and play it again though.

If you can deal with the fact KoA isn't challenging then I would definitely recommend that one.

If you have friends -> Torchlight II
If you don't -> Assassin's Creed IV Black Flag

Black Flag for pirate stuffs. (Rogue has improved gameplay & variety but more expensive)
Torchlight for Diablo-like and multiplayer (more fun if you have friends playing)
Amalur...seem medicore.
AC 2: It's alright. (But brotherhood's better, imo)