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At first when you pick up the game and look at it, the changes aren't that noticeable, but after playing it for a while you will start to notice tiny little implements they've put in the game. The gravity of how things bounce, hit and levitates on the field are all tweaked to either be more realistic or to keep a certain flow in the game. Some might say the looks of Fifa 09 has gotten worse because of EA removing the plastic look of the players in 08, but the truth is that it looks just as fine or maybe even better from certain perspectives. Either way it is debatable.
The game modes are pretty standard this year, but some of them with altered options. I.e: The Be A Pro mode now supports 2-20 player online play and of course the new Adidas Live Season which provides weekly updates on stats and how well the real football players are doing that specific week, which naturally makes that individual player suck in the game, if he plays poorly in real life. But you will have to pay for this service.
Single-player experience can get tiresome after a while, reason being that the CPU becoming rather predictable (All depends on which difficulty you are playing) so the one thing you should be checking out is the online experience. Meeting unpredictable players constantly forces you to be better and always brings you back for more. The BAP-mode isn't all that fun because of everyone wanting to get the ball and score and it gets really frustrating. So if you are looking to go online the ranked matches 1v1 is the best way to go if you're playing with friends or random people. Be sure to pull of some quite funny and spectacular player-controlled celebrations when you crush your opponents just to let them know that you are the supreme being.
Long time Fifa-fans will undoubtedly buy this game, but if you are new to the football (also known as soccer for you Americans) and you're struggling to decide over FIFA or PES, Fifa is definitely the game you should buy. Just remember that the multiplayer in Fifa is it's strongest part. Sure it has some minor frustration moments (mainly referee decisions), but that's pretty much overweighed by the more faster, realistic and entertaining gameplay.