A significant improvement over the original Bad Company.
The single player is much improved. The story and feel of the game take on a much more realistic war feel than the often cheesy first game. Single player will take about as long as one would expect from one of these war games. I would say roughly about 8 hours.
The multiplayer where most players put in most of their time is also improved. The ranking system is somewhat like COD where you are unlocking new guns, sights, attachments, etc. A player will need roughly 2000 kills to unlock everything. There is also now a team deathmatch well sort of. It consists of 4 teams of 4. There is also one tank on each map that is important for victory. There are only 4 maps to be played on so this mode doesn't have the longevity of the COD series. Also where there are 4 teams you may experience a few unfortunate spawns. Of course you have the other modes that are more familiar to the battlefield fans. There are plenty of guns to choose from and 4 classes to choose from.
Overall a fun game that is much more realistic than MW2 but also doesn't have quite as good an engine and not a true team deathmatch. This is why they score the same. MW2 basically slipped back from the first one and BC2 improved.