The game has a lot of promise but ultimately fails because of their business model.
Its not a mmo as adverstised but an online tank fps. Currently the only gamemode available is a sort of teambased deathmatch. Its based more on tactics and teamwork than fast reactions. In the first few tiers (levels) the game feels like a refreshing take on the traditional fps games, but once you start to get the higher level tanks the problems quickly become apparent.
Sadly most of the problems with this game is intentionally made this way to force the players to pay for the game.
Now for the bad parts:
The first thing you notice is that once you get to tier 4-5 the tierspread of tanks becomes much wider. That means that if you have one of the lowest tier tanks there are a lot of tanks that you cannot do any damage to, while they can blow you up in one hit.
This is made even more annoying by the "upgrade" system. Basically when you unlock a new tank, it will be severely gimped. Instead of having fun trying out a new tank you will get one that feels much weaker than the last one you played. This is when you realize you have to grind a large number of matches in this gimped state to get the tank to a point where it can be competitive with tanks of the same or lower tiers. Since the xp you get is mostly based on damage you will also get a lot less xp/match until you have it fully upgraded. Wargaming calls this process customisation, but in reality its a series of upgrades you have to get in order to get some use out of the tank.
To slow your progress down even further wargaming has decided that higher level tanks should not make credits, so you have to have lower tiered money making tanks to support your higher tiered tanks.
In other words, the game has a very very boring grind that can to some extent be made easier if you pay. You can pay to get more xp and credits, pay for premium tanks that earn more credits, pay for premium ammo that can hit higher tiered tanks for more damage etc. And suddenly the "free to play" game is a very expensive game.
The maps are all made in more or less the same way, forcing the tanks to go down one of 2-3 "corridors". That means you will always meet the enemy team at the exact same choke points that favours one type of tank, the heavy's.
Wargaming brags about the clan wars, but atm that is only available for those that have one of the top tier tanks(tier 9-10). In other words you have to grind for months to get a tank that will be allowed to participate in that part of the game.
The game is also very luck based. Even with careful aiming you never really know where your shots will hit and if they manage to do any damage or not.