Zipping around at hyperspeed and shooting feels great. There are a few things that take away from it though. The dungeon is kind of cramped, bigger open areas would make the speed shine as well as making it easier to engage enemies. The fact that you can't see very far considering how fast you're going (and even more, the edges between zones) also discourages you from going fast since you might run right into an enemy.
The dark crosshairs is hard to see against the background, but that should be easy to fix.
I bought the machine gun from the store, but it didn't seem to change my attack style. You were supposed to just left click the weapon in the store, right? If you have to equip it somehow I couldn't figure out how to do that.