It's honestly one of the few genres i'll even play on a phone. Try out games like Danmaku Unlimited 2, Dodonpachi Resurrection, Espgaluda 2 and I'm sure there are a lot of others. It's one of the few circumstances where it feels like it could actually be an improvement in control. When using a control for shmups, it's the same static speed. Using your finger, you can obviously move at different speeds and it allows for the bullet hell games to be even more filled with bullets because you're more capable.