I couldn't say a bad thing about this game.
Tons of maps, lots of weapons, lots of vehicles. There is a lot here to enjoy. I played this game a ton. It has to be the best online shooter out there for PC. The best (that may change when Bad Company 2 comes out, though).
The maps are pretty diverse. They have lots of room for tactics and sniping and vehicles and all that. There's always room for every class on every map. And the maps are HUGE. You have tons of buildings, sniping spots, airfields, command posts, vehicle spawns. It's really great. And you can shrink those maps down for tighter battles, but even then, they are still pretty sizable (you can still snipe on a 16 player map, no problem).
The vehicles are great. You have the tanks, the cars, the Black Hawks, the jets. It's great. Although the spawns for jets and helicopters are usually crawling with team killing noobs who are desperate to get into a vehicle. I've only flown a jet about 6-7 times. Although other vehicles are usually always open, there are lots of spawns for the other ones, usually about 3 per command post on the 64-player maps.
Singleplayer is..... a timekiller. The AI is weak. Very weak. Even at their hardest. But it's fun at times. It's just this game is meant for online. Singeplayer is there to be there.
There aren't any kooky infantry functions or anything. Just the basics. But there are lots of weapons and such that make the infantry game a ton of fun. Later patches removed any cheap tactics and bunny hopping (you can still do it, but in the latest patches you can't shoot while jumping, so it's really a straightforward, fair infantry system if you patch the game. All the classes are really diverse and all have their benefits to the team.
The squad system is nice too. With VOIP enabled and a good solid squad you can really kick butt. But generally people just join squads for no reason. So it depends on the server. Make sure you are updated to the latest patch. That's the real key here.