Ran into navigation issues, and got stuck in the ground, in level 3. Ranged-attacking seems far more powerful than melee. I could never quite figure out how to rapidly decrease my current heat aside from not moving, and not moving isn't very fun. That said, it seems like heat just does some damage and resets, so I typically ignored it.
Aside from these points, I had a blast playing. I enjoyed the skill required to get rockets to arc to the right target and hit at range, and most straight-shoot-y weapons did enough damage to avoid being tedious to use. I did have trouble enjoying the Warrior loadout, between the melee and the kinda dull pistol-like weapon, but with the ability to mix and match loadouts that doesn't seem like a real complaint.