I hear Battlefield 3 Blows Modern Warfare away.
BF3 is definitely a different style of gameplay. Larger maps (way bigger) with many more variables in the shape of character kit options and upgrades, vehicles (jets, helos, tanks, jeeps, boats) as well as emplaced positions and longer games allow for more strategy and tactics than CoD. Add to this some game types that really require strategy and teamwork to accomplish. If you try to play it like CoD and are just sprinting towards the action every time, you will not do well and the game will not be very fun. Study the kits and make maximum use of the special abilities and equipment they have to offer and play them accordingly. The trick is finding a team that all think that way using different kits that all support the team in a different way.
There are some aspects I don't like about it. For one, explosives are WAY under-powered. From grenades to tanks this is an issue that a lot of people are complaining about and the folks at Dice will hopefully address.
Another annoying aspect, to me and many others, is that when a game is done you cannot back out of the lobby until the next game has started. Only then does it give you the option to quit. Nor can you tweak your kit in between games. Like I said, annoying, but hopefully there is a fix coming with the next patch update.
So, yes, in many respects, BF3 blows MW3 out of the water. Especially in breadth of gameplay and options. So if you're looking for a quick, easy to play FPS then CoD is for you. If you want to sink your teeth into a game that has a steeper learning curve with many more options then I fully recommend BF3.
Me? I play both depending on my mood.