Quite a few changes from the PC version, but still worth playing/ buying if you have Xbox Live.
Xbox Live is VERY different to Offline Single-Player. Online mode is the good-old conquest like gameplay from the BF games on the PC. Once you've picked one of the 5 classes and spawned in the map, it's your job to capture and hold the flags (which act like spawn points) and protect them from the other side. First team to capture all the flags wins. However, like BF players already know, each side start off with an amount of 'tickets', which go down by one whenever someone dies, or if a team has just lost a flag and now has less flags than the other team. The action in multiplayer is pretty intense, and is also very fun.
The classes in online mode are exactly the same as offline mode, I'll list them here, because there are a couple of things that where changed since the PC version:
Assult: jack-off-all-trades, carries an assult rifle, the most newbie-freindly class :)
Special Ops: For stealth and stuff, with added C4 goodness
Engineer: This is weird. Can repair veichles, but also blows them up too with an RPG launcher and mines. A mix of two classes from the PC version.
Sniper: Name says all, carries a Sniper Rifle and can be very annoying when used in the right hands.
Support: Your average Medic, but with a big machine gun to boot. Also a mix of two classes from the PC version (I think)
So theres enough varaity in the classes, and NO class owns all others, they are all pretty balanced, which is always a good thing. There's also plenty of people still playing on Live so its not like your gonna be waiting for a game that suits your tastes. The main problem with Multiplayer is that its the least Newbie-Freindly online game I've played in a good while, and because you cant practise the maps with bots or anything, most new players will find themselves a bit lost at first, and might be put off (hell, I was), but just stick with it because after some getting-used to you'll be enjoying probably one of the best Xbox Live games on the console.
The graphics in the game are....varied. On one hand, everything looks fine. Weapons look good, and their appearence changes depending on what side your playing as (China, USA, MEC or EU) and the maps are pretty detailed. But, when you die, you'll notice that as your guy falls to the ground, the people you play as look ugly. And before playing this game, I thought 'Ragdoll' physics was God's gift to gamers everywhere. Nope, somehow EA have managed to cock up Ragdoll. The bodies have mini-spazms when they die. However, you'll only notice this when you die, the actions usually to fast to notice this otherwise.
Overall, great game, but take off 3 points off the score if you dont have Xbox Live. And another point if you cant stand badly-done Ragdoll physics. :P
Apart from that, a great alternitive, if your PC cant run the PC version of Battlefeild 2.