Apparently I'm among a thread full of people who never played Battlefield 1942 or Battlefield 2 back in the day.
Bad Company is a spin-off, it is a mini-me version of the original Battlefield series. Notably smaller in scale, and missing a lot of details that made the BF series great. Battlefield 3 is a sequel to Battlefield 2 (2005). It was a PC-only game, never ever released on consoles. Consoles today can in no way handle even Battlefield 2 as is, and that was 6 years ago.
Battlefield 3 is being developed primarily for PC, and a different version (noticeably scaled back) for consoles.
Jets, helicopters, many other vehicles, very large multi-terrain maps, 64 players and cohesive teamwork.
They're also whipping out the Frostbite 2.0 engine, which should be absolutely phenomenal. There is going to be a Lot more destruction. You can blow craters into the ground for cover, buildings topple in more advanced ways, and generally the engine can handle a lot more. Will also feature radiosity, which is basically an advanced lighting system. You'll see flickering lights inside buildings when they're being shelled. Light will bounce off walls, tracers will radiate light possibly, etc. Plus all the other eye-candy, that just looks nice, and is effective for proper atmosphere. Newer DirectX features with smoke/fog volume, lighting, distortion, all sorts of tasty morsels.
This is all meat & potatoes stuff for the PC. I won't speak for consoles, as I don't care and have no idea. They're not meant to handle BF3 at it's best. It will be an advanced engine at the very least, considering DirectX9 cards will not even function with the game, meaning not even Windows XP compatible, as far as I know. DirectX10 & 11 featured, amazing.
Also, an even better sound engine. DICE's sound is always incredible. I'm excited to say the least.
I like Bad Company 2, but it's far too small in scale. Maps are too small, and tactics are shrunk, so it's still possible to turn the game into an shoebox arena-shooter. Original Battlefield series was always just a 'tad' more complex, and a bit more needy with teamwork. So you always ended up 'holding the line', great firefights, flanking tactics, etc. It's hard to do in Bad Company 2, because everything is virtually a miniature version of it.
It's nothing like "every other shooter"... I kinda feel sorry for you folks, because you clearly haven't been spoiled enough. It's gonna be good times running building-to-building with a good squad, taking cover from bombing runs, clearing streets, and looking for that damn sniper. All I can say is, my PC is ready.