With Elizabeth in BioShock Infinite though They created the best AI companion in any game ever.
The developers did a really good job you really start caring about her. You Should Watch "BioShock Infinite - Creating Elizabeth" If you are interested in the process.
Like i said before she is probably the most interesting character in any game lovable, if you have played "The Last of Us" and say but what about Ellie? Yes, Ellie is awesome but really to be honest Elizabeth is even better.
The graphics and style of the game is really awesome as well, but it is the story That makes it so incredible.
The only think i could say something negative about is the weapons, the only good ones are Actually the sniper and maybe the revolver. The sniper is almost all the time a one-shot kill and i would advise the player to never let go of it, since it is not that frequent of a weapon.
If you have not Played it yet i strongly advise you to do so :)