MP hasn't really changed for any of the BF games. So, here's the release schedule:
2002 Battlefield 1942
2003 Battlefield 1942: The Road to Rome
2003 Battlefield 1942: Secret Weapons of WWII
2004 Battlefield Vietnam
2005 Battlefield 2
2005 Battlefield 2: Special Forces
2005 Battlefield 2: Modern Combat
2006 Battlefield 2: Euro Forces
2006 Battlefield 2: Armored Fury
2006 Battlefield 2142
2007 Battlefield 2142: Northern Strike
2008 Battlefield: Bad Company
2009 Battlefield Heroes
2009 Battlefield 1943
2010 Battlefield: Bad Company 2
2010 Battlefield: Bad Company 2: Vietnam
2010 Battlefield Online
2011 Battlefield Play4Free
2011 Battlefield 3
If you played DC, you basically played BF2. I've played every mainline BF game. If you want to see innovation, go play 2142. They backtracked from it because it was too different. People just want modern war games.
I get that people are tired of CoD. It's been on top for so long now. If you're not a big fan of the series I completely get how it just feels like more of the same. It mostly is. But so is everything else nowadays, battlefield included. The last truly innovative FPS that actually had some popularity was MW1. Maybe BF3 will have some sort of critical mass of new players that the last dozen BF games didn't, and it'll feel fresh to a brand new audience. I hope it lives up to the hype. But it's still a rehash.
I agree with this
I've bolded the above that weren't full cost though, that were released either free initially or eventually, and were just sold as expansions/DLC. I think that's what irks some of the folks, that the differences between major CoD releases have become much more like the BF expansion packs, but they still want to sell them annually for 50-60 bucks. And now they've found a way to charge what, $100ish for the 'elite'?
For the people that really like it, that's fine. I can understand. I had sooooo much fun back in the day playing lots of twitch shooters with smallish maps, Quake, Quake2, Quake3, UT, etc. I appreciated the various games that gave more options in terms of vehicles, map sizes, classes, etc. Tribes was a lot of fun, ditto the BF series. One thing that you notice quickly with those type games is how important it is to play alongside people that know what they're doing, and to organize teamwork more. That's a double-edged sword, as a good match might take half an hour or more, and having crappy teammates can ruin the fun pretty quickly. That's hugely different from being able to jump into a DM game like MW and just go on a killing spree immediately within the first few seconds. With the attention span and average player quality ou there, this makes a lot of sense.
Back to CoD, I think everyone but their stockholders would be a little happier if between each release they had a major DLC pack or expansion pack ($25ish) that brought everything but the SP campaign as new, and then every two years you got a full release with a new engine, new SP campaign that's twice as epic, etc. Unfortunately it seems like if anything, we're going the opposite direction, and will end up having to get a new MW game every 6 months that will have even less change to it. I'm sure they're desperately trying to figure out how to EOL past games now so that they can herd more people into each new one more quickly.