Great Game
I'm afraid I can't give too much in the way of unique suggestions, since I mostly agree with those that have reviewed before me, but I'll go ahead and add my two cents anyways.
As I'm sure you're sick of hearing, the zombots were insanely difficult, but I found by using strategic hammerstrikes and lunges I was able to get one alone and take it out. This was very finicky, though, and I think in addition to adding the "fast zombies" (along with some other types, like the "slow zombie" and the like) an area of affect ability would be appreciated, maybe a ground pound.
One thing I think you should avoid in the sequel would be combos. I feel they are over-done, and often stop a player from using 6 regular attacks and instead use the 2 or 3 combos. The system you have set up allows for what feels like player made combos, which are very satisfying to pull off: punching a zombie twice, kicking it to the ground, and then stomping on its head.
Also, I enjoyed the point mechanic for buying new suit types, although the speed-suit seemed a bit underpowered. Maybe upgrade so you can use points to buy/improve different attacks or regeneration rates? Just a thought.
Anyways, love your game, going to try and get that mining suit finally.