Absolutely not. Its a good Halo game, but the single player has a much weaker 2nd half and the characters are poor. The multiplayer is good but the map quality was low compared to older releases. Its a good game don't get me wrong, but not the "definitive" game of the series.
Just my thoughts, but Portal 2 can be gotten when its dropped in price later in the year, and same goes for LA Noire. If your liking the Witcher and want more straight after your done then get that but from your description of your love for Infamous I think you should get Infamous 2.
I loved them both and had a great time playing through them. I thought that the increased role of factions in nv was a big improvement over fallout 3 and that nv story was better, but I preferred the locations in fallout 3. What did a lot of damage to nv in my playthrough was the bugs, far more than I experienced in fallout 3. If the bugs hadn't been present it could have been a different story, but I feel that fallout 3 was the more polished and tighter game.
Im sure that pc games run better and all that, but honestly I cant tell the difference when Im playing the vast majority of games. For my hard earned cash Im very happy with the current consoles and don't want to buy a new generation of them for at least a few years.