This is game awesome sauce.
http://www.worldoftanks.com/Basically its FPS with tanks, which is mostly historical having tanks from era '30s - early '50s.
They control like a lightning from Planetside, though the similarities end there. The game is complex in that it has hitboxes, deflecting shots based on armor slope and projectile angle contact, gun caliber vs armor thickness etc. Another such effect of hitbox play is targeting a tank's track wheels and dismantling their track to get on their ass and blast them.
You start with an early '30s era tank, and through exp gain and credits earned, you can upgrade your tank's equipment such as gun caliber, engine HP, or eventually upgrade to a new tier. As of the beta ending last night and going live, There are now 4 nation's tanks to choose from: U.S., Germany, USSR, France.
You can play all of the nation's tanks on a single account, and not have to be restricted from others.
Not only are there tanks, but also tank destroyers, and self propelled guns (artillery). Each of the three has their own playstyle, and artillery is it's own niche in that when you go to bombardment view, its a live overhead view of the battlefield which allows you to lob shots in support of spotters.
And as mentioned, as you progress you can research and gain access to more advanced tanks. i.e. progressing through a series of Panzers gets you to a tiger tank, and that tiger tank can research into a tiger II tank etc. There's a total of ten tiers, with each tier battling with tiers one above or below them, so theres no instances of a tiger II tank smashing down on a 1930's tank or such.
There will be disadvantages if you put yourself in one however, such as trying to frontal gun duel in a tier 10 medium tank vs a tier ten heavy tank etc. Though if you are wise, you could flank a heavy tank and attack its weak rear armor.
Its not like a WoW or other mmorpg type grind where you want to get to the highest tier for endgame content. Its more like you would have many types of different tier tanks and other vehicles to enjoy playing with, which is what everyone does.
The game is F2P, so you lose nothing trying it out. Premium "cash shop" purchased items don't really give too much of an advantage over free players, so its not overpower concerns. Actually the game gives you 250 daily premium currency to be used even as freeplayer, which can be used for things such as premium ammo, transferring exp etc.
Some screenies: