Took me about 8 hours in total to get through the BF3 Single Player Campaign. The combat's great, the graphics are absolutely incredible, and the game technically runs just-fine (over 30 FPS most of the time, according to FRAPS in 1920x1080 w/ most stuff all the way up) on my rig...
...But, the story feels like someone threw the story of COD4: MW and MW2 into the Battlefield games! Did I like it? Yes - it's good, but not great and not innovative at all. It's...missing what makes BF series what it is and always was - expansive, wide-open, free-form sandbox gameplay (in a contained mission, map, & ruleset).
Then, there's the Multiplayer - which is the absolute complete OPPOSITE of the SP. This is where it's at, folks - it's flat-out AWESOME. You probably expected that. The maps are HUGE. The MP itself feels more open, wide, expansive, and feels very free-form in its combat, pretty much. Sure, there's a TON of different game-modes and whatnot - with different rules - and you play within the rules. In Conquest Mode, you can jump in vehicles, jeeps, buggies, F18 hornets, tanks - and just go out and do whatever the objectives are and frag enemies. It's a blast and looks like a full-blown full-scale war. Of course, I've ALWAYS loved the all-out team-based frag-fest in Team Deathmatch - I've always been a fan of Team DM (and normal FFA DM, even though it ain't in BF3), in most MP games. Team DM is a blast on here, as well - especially when the servers are loaded w/ players.
If only the SP was as interesting, open, and expansive with its gameplay like the MP....