I know I'm going to be at odds with everyone here, because for me it does so many things I want it to, and does them very well.
99% of my games are online; while Master League used to float my boat, it seems a bit redundant now online modes have been added - I can't seem to play an offline game without that nagging feeling that I'm missing the opportunity to beat some real opposition.
I still play this regularly - my 360 blog shows that I've played this nearly 1 day in 2 since it's been released last October, and that for me is just head and shoulders above any other game I've played to date, let alone other football games. It is simply the best football game I've ever played, and is a good progression from the previous iterations in the series from a gameplay point of view.
Fundamentally, PES6 plays a damn fine game of football. I mean, for 90 minutes on the pitch, you can express yourself, and generally, the better player wins through skill and judgement. Glitches are few and far between, and the ball physics just feels right to me, I can read where the ball is going to be. The players make intelligent runs (except they go offside too often) and the formations allow for clever tricks to fool the opposition.
That said, there is room for improvement. More online options - 2v2, tournaments, player rosters, better stats and rankings would all have been relatively easy to implement and have added alot. Better player differentiation would have helped too - Adriano was just so strong it unbalanced the game, and the 'weak' club sides were too weak. I didn't really miss the edit mode, as like I say, I play online so modifications aren't allowed here for understandable reasons.
From my point of view it plays well for short bursts, but is maybe a bit shallow. A bit of a Dannii Minogue, you might say.
8 (Excellent)