This game stops just short of being great
This game a lot of potential with some work.
I'll start with the scoring/money. I'm not sure why you would make the two of them the same thing. If this is a "highscore" game, then why would we want spend all that time collecting money for upgrades only to have to keep on killing the same monsters over and over? If this were a scrolling game with different levels and bosses then I'd understand. And the upgrades are far too expensive especially if I have heal myself every other level OR completely restart if I die.
As for the game-play itself. Well. I saw that you addressed the fact that the character moves slowly. You suggested jumping over the zombies. This wouldn't be a problem if you didn't have monsters that leap or run. I dodge one zombie only to run into another. Then there are the grenades. The window is either not wide enough or he throws them too slowly. There is no sure way to land a grenade if I'm being jumped at/rushed.
Things that I believe would greatly help this game:
-Wider game-play screen
-Faster grenades
-Stronger knife
-Higher jump
-Separate score/money
-Either more money from kills or cheaper upgrades
-Bosses?