There are several different enemy classes to deal with. (videochums.com)
Levels last anywhere from 10 - 20 minutes to complete successfully, and each level adds a new enemy class and corresponding weapons and upgrades to the mix. (roadtovr.com)
Features 16 playable classes each with 9 abilities and 30 + enemy classes with their own 9 unique abilities. (allpcgame.net)