The faction system is actually the best part, if you think of it as daily/weekly reward instead simply... it's how you can actually get everything without paying to win.. and literally everything.. in due time... a few weeks and you won't really have money issues for main team, level 5'ing them.
I would dare say that girls on tanks is one of the friendliest games for free to players - you literally get EVERYTHING for free... and if you bother playing faction wars daily for girl exp and getting the weekly epic box - you get top tier stuff in no time.
i would say the balance there is rather okay and it's fun to complete the game if you enjoy the grid turn based tactics..
There is element of progression, there is positioning, there is everything... the only real flaw is the amount of content IMO... and you can't really design anything interesting event wise there... so yeah. It's certainly not a great game, but a very decent one, can be considered pretty much a free single player game tho.
The only potentially good change I can see on it is adding live pvp there.. but I doubt it will be done.
Getting everything for free is much easier than on crystal maidens, that's something I can guarantee(have main team and substitute team on girls on tanks leveled to max outside of the ones who are better off low level and most of the stuff 3 star'd - no payment involved, not even free sign up stuff)
But I can see how there can be much hate for the game - grid turn based strategy is one of the most unpopular genre of all... mostly favored by the older audience.