The latest and greatest version of Battlefield actually has a single player game. It's also on console in its full multiplayer glory, and not an uprezzed port from a last-gen game.
I can't say I liked Battlefield: Modern Combat all that much. I really wanted to like it, because I couldn't run Battlefield 2 on my PC at home - but its awkward mix of arcadey game conceits and realistic military combat never sat right with me.
It's a shame for them that they didn't get the balance right, because a couple years later, Call of Duty did more or less the same point accrual system and worked out the kinks. Bad Company gets it much more like Call of Duty, and as a result is a huge step up from Modern Combat.
The other "hook" that B:BC has going for it is destruction. Almost every wall can be destroyed with enough high-explosive, and the mechanics work like a charm. On top of that, it really *feels* like you're laying waste to huge environments, and has pretty substantial gameplay ramifications. No longer are walls guaranteed cover, no longer are long-distance snipers safe from rocket fire.
The multiplayer is fun, frantic, and evolves substantially over the course of every match due to a progressive map-unlocking structure. As you play, if one team achieves their goal, another portion of the map unlocks, the defenders fall back, and the attackers press their attack. It's great fun, and the constant medal award system keeps you hooked for just one more game.
The single player's a bit strange. While again, it's leaps and bounds above Modern Combat, and mechanically, it's as sound as any other FPS out there, they strike a strange "lighthearted" tone throughout the game. The characters are constantly spouting jokes (to limited success, though some of the background animations are *really* well done), and talking about very cliche things (If Sarge makes it to the end of the game with his constant talk of retirement, I'll be really surprised) - so it's clear that you're supposed to take this all with a wink and a nudge.
The problem is that periodically, something like having an allied helicopter or patrol blown to smithereens right in front of you breaks the lighthearted tone, and reminds you that people (and not just the enemies) are being killed. It's a difficult balance to strike, and while for the most part, the game's story works, it periodically veers into the unintentionally grim.
Overall, between a fun, engaging single-player game and a ridiculously entertaining multiplayer game, Bad Company's definitely worth picking up if you're done with Call of Duty 4... or even if you're not.