I was quite skeptical of this game when I first heard about it, but was bored and so downloaded it. I was a bit disappointed with the first tanks you get, but by tier 3 and 4, I was having a blast. Each class of vehicle plays differently and learning that can be very frustrating, but also very rewarding when you find your niche.
I originally gave this game a 10, but have to back that off to a nine for four reasons:
1) Game stability fluctuates. Several releases simply crash. Lately, after playing a game and starting a new one, the game will suddenly exit.
2) Matchmaking often leaves much to be desired. It's not much more fun to be in a team that wins 15 to 0 than being in the team that gets demolished. It seems that a big, perhaps unsolvable, problem is not balancing teams between defensive and aggressive players. That said, when the balance is right, the fun level goes way up.
3) At higher levels, playing can become very tedious, especially if you have a bad tank that leads to a good tank. The grinding gets very tiresome and, honestly, does no favors to your teammates.
4) I started playing self-propelled guns and found I was very good at it. Then they nerfed them. Most of the nerf doesn't bug me, but the accuracy does. At times, even when you've waited and let the targetting settle down, shots seem to become completely random. Yet, next game, doing the same thing, you shots are dead on.
I highly recommend World of Tanks, though do suggest to not be in a hurry to get to the higher tiers.