the single player game is good, although the plot seems a little thrown together. As mentioned the graphics are amazing, especially in HD. the game can be finished quite quickly unfortunately, although the final boss is very difficult if your playing alone. The AI for the computer players can be very stupid at times.
Personally i would recommend you rent this game and see if its for you, then consider buying it.
Online i feel its very weak, there is a severe lack of realism in the weapons, eg you can unload a full clip from the rifle into someone and not bring them down. For this reason i've never played it online much and never will do.
don't let my review put you off, there are many good points to the game to, the reload system is very good, as is the use of cover. Although this later point is put to much better use in rainbow 6 vegas.
To summerise...
It was not in my opinion all it was hyped up to be, although the graphics should definately be experienced. could i warrant the £37 price tag then... I'm afraid not. Rent it for a fraction of the price.
Cheers,
Matt.