It was actually pretty easy to pick up, but it's still tough, which is a good thing. It was fun shooting around, but I felt like the difficulty was more based on enemies spawning rather than their AI. It wasn't a bad thing and I actually enjoyed it because it keeps you on your toes, but I also would like more enemy AI variety in the future. Also, a shop/skills/upgrades would be nice to have if that wasn't already suggested.