I hesitated pretty hard at the price tag. If it had been $5 or something I would have gotten it without a second thought, mostly because (while I love Warband), I didn't care much for Fire and Sword. That, and this era of combat isn't one I'm particularly interested to play in.
Having said that, I've been playing on and off when I have the time. Several of the largest servers are frequently full, though they usually have 5-15 slots open (out of 200) when I launch the game. There are a number of game modes, including siege, conquest, battle, deathmatch ... I've stuck mostly with siege and battle.
There isn't any single player content to speak of right now. You can do as Catastrophic lolcats suggests, but it isn't as engaging as it could be. Unless and until they add a campaign or something (and they should!), I wouldn't get it just for single player.
The huge 100 vs 100 battles and sieges are downright awesome fun, though. Some pre-made groups form actual battle lines, complete with standards and musicians, while most everyone else runs around and has fun with the tragically inaccurate weapons of the era.
The rockets are probably the most astonishing team-killing weapon I've ever seen in a game. You'll see guys carefully line up a shot on the enemy, then ... fWOOooooshzzzzziiiiiBOOOM! It spirals crazily all over the place and strikes a cluster of friendlies hiding behind a rock, 50 degrees and a long walk to the left.
The graphics and sounds are well done. I love the crack of the muskets and smoke that conceals the battlefield for a moment.
I'm a little worried server pops will drop, too, because then it won't be nearly so much fun. The hilarious antics are as entertaining as the Actual Point of the Game.
Really, the only reason I bought it initially was because of how many hours I've put into M&B. But I feel like I've gotten a great amount of amusement (and Fun) out of it over the weekend, so no regrets.