One of the first five gacha games I've played.
In the past the game is grindy as heck it can take months to build a high level team, today they improved it so much that it didn't take as long to build one anymore but by today's standard it is still pretty grindy.
With exception of events limited characters that can only be get by redeem it by shop or get lucky on an Event stage the only way to get characters for this game is by putting resources that can get mostly in game on factory with set amount to get specific roles like snipers, machine gunner, etc and depending on luck you can get high rarity one. The only thing that is remotely close to your typical gacha is the Skin gacha which one with furniture gacha.
The game are 10 years old so don't expect amazing graphics, but art styles is still hold up well.
The early story chapters are mostly not good in term story telling but it gets better starting around episode 8.
Gameplay are definitely not for everyone because most of the time required you to plan Smartly, manage your limited resources wisely and build your team effectively because if you use it recklessly you will hit a massive wall that can take months to overcome. For the combat you need to be strategic because while the game gave tons of repairs tickets compared to the past you can still waste too much of your time trying to finish a stage especially on a harder one.