ShooMachi

This game is my most played shmup on android and in my opinion, possibly the best. The base game is not very long, but after you beat the first rank you can keep playing at rank 2 and unlock different characters and SO many different skins for them that have bonuses like extra xp or gold or health, even a smaller hitbox, it's awesome. I think this game has a great difficulty balance for newbies and veterans. It stays fun even when it's easy and it ramps up and gets really intense at later levels. The patterns and enemy formations are just so much fun towards the later stages. My favorites so far have been 2-7 and 2-8, which I literally just played. they just keep getting better.