Tbh, I wouldn't say that it sucks, more that it's "almost fun." Overall, it's a pretty solid game, but there's also a lot of questionable gameplay/economy balance decisions that have been made over the years. For example, balancing OP tanks/aircraft by making their repair costs so incredibly high that you'll wind up loosing SL if you die, no matter how good you actually did in a given match.

Battle rating compression is the other big issue. Basically, the BR balance is overall designed with the goal of getting players into matches as quickly as possible, which results in the BR spread being such that there's always plenty of vehicles within +/- 1.0 BR from the BR of the vehicle(s) you are playing. As such, this results in a lot of cases of WW2 vehicles fighting vehicles from the early/mid cold war, which is fine in some cases but frustrating in others. It also results in cases where certain vehicles are OP at their current BR, but bumping them up just one BR bracket results in them being completely useless (and also vice versa, where a bad vehicle can't be moved down 'cause it would be too OP).