Yup!
It's one of the better cell-phone games. Doing story missions doesn't consume any stamina-type resource. There's another area that gets you various rewards that does consume stamina, but since the two areas are separate, there's never a feeling that you've run out of things to do.
The multiplayer aspect of it works pretty well too. You're only limited to host five games per day, but you can join in as a guest an infinite amount of times. Doing multiplayer gets you various rewards you can't get from story mode, so there's good incentive to do it once you get to Lvl 50 on one character.
The gacha system is pretty manageable. The resource you need to do it is plentiful enough that you will be able to make use of it on a regular enough basis to get the high tier weapons from it. The gear you get from it is the best in the game, but one you get it on enough characters, it can carry you though the rest of the game. The gear that's most likely to drop from it changes every week, so you'll want to save up the resource for it until the character you want gear for pops up and then spend it on that gatcha until you get however many copies of their weapon(s) you want. You'll more then likely get weapons for other characters while doing so.
So yeah, paying money will obviously get you stuff faster, but it's not like you have to pay money to feel like you're getting anywhere either. Which for a FTP cell-phone game is great.