This should probably be moved to the arena...

I agree that you can't go wrong with the halo series. I haven't player Halo 4, but Halo:Reach was a lot of fun online. As for RPGs, my favorites are games by Bethesda softworks. They come with deep, immersive worlds that literally contain lots of locations for you to explore and loot, lots of characters, lots of quests and lots of items.

Although I aren't really sure you should buy games for current consoles with the next generation about to hit the stores.