Mass Effect is an amazing series. The ending isn't what everyone wanted, but the Extended Cut DLC (free) really sweetens things up. I was 100% satisfied with the way my game ended once the EC came out. All this to say: Get it noooow.
Bumping this thread up since the PS3/360 gen is winding down. What wound up being everyone's favorite new franchise from that generation of consoles? I think I'm leaning toward Mass Effect moreso than AC now. AC3 was godawful and pretty much killed my love of that series, especially since it's being milked to death. I'm finally playing Mass Effect 3 now and enjoying it, though not as much as 2.
Mass Effect and the Batman Arkham games for sure. Of the new franchises I played last gen, these are the ones that really felt next gen for me. They were epic and expansive and cinematic and entertaining from start to finish. Batman was like nextgen Metroidvania especially. Both franchises were highly polished. (And not consoles but as the DS was last gen... The Ace Attorney and Professor Layton games are wonderful and delightful and fun and quirky)
Without a doubt, Mass Effect. Geoff convinced me to get the entire trilogy, and if I hadn't gotten it, I would have no clue what to play on my days off from work. I'm currently playing through the second one right now, gearing up to hit that Omega-4 relay by scanning every planet for resources and doing loyalty missions, and I'm having a lot of fun with it. I'm very cautious when it comes to sequels, as they normally seem to be copy and paste versions, but I was pleasantly surprised with this one. It continues the story, polished up where the original Mass Effect fell short, and I really like the characters. I'm going to be so heart-broken when I finish the series and realize I'll never go on another mission with Garrus by my side the same way again. Honorable mentions go to Portal and The Elder Scrolls. I know The Elder Scrolls have been around for a long time now, but I'm specifically talking about Skyrim. That and Portal 2 have brought me back into the realm of gaming, and I could play those games until the day I die.
Souls series; though I'm yet to play Demon's Souls so apparently I'm not a hardcore Souls junkie until I have that under my belt. It's one of those awkward games that never appears in local shops, kinda like Paper Mario for the N64 back in the day. :(
Ooo, I didn't think of Portal. Portal series is great. It's like we've had four campaigns of it too between the original, the nearly-official map pack, Portal 2, and Portal 2 co-op. A lot of great ingenious content there.