Borderlands!

It's a FPS with RPG elements but it's a great game nevertheless! Make sure you get the GOTY edition with all the DLC's. You can play Borderlands in co-op with four people (you + 3 others) and there are a lot of fun things to do.

What do you see as "next-gen"? Games that were released on the Xbox 360 / PS3 (I play on the PC mostly)?

My top 5 games would be:

1. Half-Life 2 (+Episode 1/2, if not, Episode 2 is #2 and Episode 1 is #3)

2. Mass Effect

3. Dragon Age: Origins

4. The Elder Scrolls IV: Oblivion

5. Amnesia: The Dark Descent

But not all of those games are "next-gen"

TESIV:Oblivion.

2nd is Dragon Age: Origins with 7 playthroughs :P