World of Tanks http://www.worldoftanks.com/
Enjoyed playing World War 2 microminiatures as a child? Liked paper-hex wargames from the SPI/AH era of boardgames? Not enough PC tank sims since Atari Battlezone? Enjoyed Steel Panthers way too much? Want to do the same in matches against live players (16 vs 16)?
Then World of Tanks is probably for you, IF you can tolerate a MMO structure that does include some grinding. MMOs basically have a carrot-stick model. You get so much fun of some type (PvP, instanced dungeons) which is counterbalanced by the developers desire to get paid, such that to be competitive, you either play ridiculously a lot, or you eventually pay into the pot.
The carrot in WoT is getting to "own" a large variety of graphically detailed, and game-detailed armored fighting vehicles, including mobile artillery, tank destroyers, and tanks. There's also a bit of RPG and leveling in that crew-members, gain experience and skills, and can be swapped at will. And the core reward is getting to play a tactical micromachines game with sim-like details, while being relatively casual in a combo game mode that is half-team deathmatch and half-base capture.
Pros: free-2-play model, with multiple premium pay-as-you-go options. Well designed game-play including cover and concealment, an artillery and spotter model, and many detailed characteristics (suspension, engine, gun, crew, extra equipment) that influence a match. Relatively easy to enjoy for free, and then to enjoy a bit more for cash proportionate to what you spend, starting at $8.
Cons: microtransactions can nickel and dime you to death if you get addicted. The release of vehicles is strictly either by premium or by "researching" a tech tree with costs that generally mean you will be spending real money to avoid miserable experience (a classic case is needing to play hours/weeks as a sucky M3 Lee (American tank that is a lousy jack of all trades) to enjoy later vehicles). Some per-pay options are superfluous and non-intutive (almost misleading) if you don't read a wiki/manual thoroughly. Some premium tanks are largely junk and unfun to play (they're basically overarmored, undergunned) and only exist for the meta-game of raising credits. The meta-game mechanism of gold, credits, experience, free experience, and researching the tech tree are fairly complicated for a new player; OTOH, they are pretty fair and help to make sure that the developers make some money while also moderating out some sillyness (e.g. they practically eliminate gold-farming, team-killing, and other meta-gaming that would ruin a typical FPS team deathmatch game.
Overall, I can tell they put a lot of effort into designing this game, with a lot of love for their game and the hopes of developing a large fanbase, rather than use a kill the golden approach that some MMOs use.
As far as MMOs go I give it a 10 for originality, creativity, bold future plans, excellent design in balancing the free2play and per-play experience, and hitting the wargaming niche market (few MMOs hit that except lamely), and a 8 overall since it has a large need for improvement (more maps, addition of alternative play modes).
If you love wargaming and like the idea of a free2play MMO, I'd give it a 10.
For being relatively early in the development cycle (post beta, but essentially at v1.0), I give it about an 8, with the score going up if the developers pull off additional fun game modes (e.g. PvE scenarios, more maps, more traditional FPS game modes).