Having played Killzone 2 I thought the bar was set pretty high for this 3rd installment.
Killzone 3 doesn't just clear this bar, it's made every fps game I own look like the designers spent 30 seconds with their assorted games and said "Yeah, that'll do".
Granted, it does only play in 720p, which is a little irratating in places because it's not quite as smooth as Mw2 and the like, but the controls are nicer, the cover system (even though it's just been lifted from Killzone 2) is good, and now (at long, long last) Rico can heal you if you charge in all guns blazing and die, making yourself look ridiculous.
The Only real quarrel I have with this game is the audio, at the beginning of the game the voices jump from one line to a totally different line that would have been further down the script, this is possibly my fault as I do tend to just charge in and kill everything in site.
Hugely recommended game, 9/10 easily.