I haven't played CoD4 or Assassin's Creed but I'm considering them. My bro has them both and recommends them.
CoD4 = XBL and multiplayer so there's a H3 alternative for you
Assassin's Creed = heard great things, open environment, gameplay, side missions, no XBL though, just achievements... if you liked Prince of Persia then you'll like this
I own BioShock and I loved it. It was a refreshingly new storyline for me with a classic feel, great voice acting and music and it offered 2 endings. I really had fun with this game... BUT, to be honest, it did get repetitive after awhile and the only way to keep it fresh was for you, the player, to just try different tactics and plasmids etc. And pitting it up against the other games you mentioned I would have to say get one of the others since there's no XBL on this either and the replay value isn't much once you play it once or twice if you are determined to get all the achievements and see both endings. Not to say it's a bad game, far from it, but you might want to just rent it or borrow it from a friend rather than own it.
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