First impression: really cool game! Looks very polished and is fun to play!
Some positive notes:
- this music is brilliant
- graphics and sound top-notch
- I really liked the pacing of rooms and waves
Some negative notes:
- only worked with a controller (not KB/Mouse)
- controls were not intuitive to me (personally), for example in Gattling Gears, just aiming the shoot-stick == shooting
- it was not clear to me why at some point my machine gun was exchanged for a shotgun or a grenade launcher. (also not why is the shotgun not autofire)
- hazards in 'double trouble' were a bit overwhelming compared to a relatively easy game before that. i'd introduce them gradually over the course of 6 rooms or so
- enemies don't seem to shoot a lot, they could definitely shoot more often
Great game, good luck on further development!