PLAYER WARNING: THIS GACHA IS BEING FRANKENSTEINED. IT ENDED IN JAPAN.

Played this since launch on and off. I don't like how predatory the gacha is, gatekeeping you from the good weapons and characters for lots of money. Honestly better off spending your money on the 3DS original, even if you've played it a million times.

Also, for a warning, the english version released on IOS and Android is a very very bad translation. It's very clearly machine translated, and it's disappointing.

I've been playing the Japanese release for about two years off and on, I recently got a chance to play the closed beta test. Overall, this game is very fun to play by yourself and along with friends. Finding friends isn't very hard, as the search function makes it fairly easy to find people who are active.
The soundtrack is nearly the same as the original. Graphics are updated to be compatible with multiple smartphones. FPS and camera view can be changed on the fly as well.
There is energy used to enter field play and other modes, however the energy is regenerated pretty quickly. Level 5 mobile games seem to be very user friendly after the first two hours of starting a game, I've never really ran out of energy or feel compelled to throw down money.
A few downsides to this game; the fact there's no hub cities that connect the fields, it's just field play once you enter combat. Also field play seems to be limited to a single day and night cycle of enemies, so if you defeat all enemies during the day, you have a set of night enemies, and if you defeat both sets of them, at the next day cycle you are left with an empty battlefield and there's no choice, but to end the field play.