1 word - Awesome!
2 words - More guns!
I think it was really really well done.
The music was cool along with the sfx.
The zombies exploding sounded like from the game Cubito Mayhem on NG.
You should check it out, similar concept.
I strictly advise you to add in more weapon upgrades, because i thought it just wasn't enough for me to survive just with 2 gun types and it seemed repetitive and you kinda feel bored after a certain point.
Because in a game as you proceed in time you marginally get stronger and gain the ability to "survive longer and hit harder".
The game wasn't hard so that actually made up for the fact you need not become stronger to survive, with just a little keyboard skills you could move and kill easily :)
I survived for 740 seconds, killed 2658 zombies and my score was: 140200.
If I could do this with just 2 gun types and 1 weapon upgrade that lasted only for a short duration.
Imagine what one could achieve with more gun upgrades and types.
I personally didn't have any issues with the reload time, that is how any gun works.
More importantly this game requires a mini map, not well designed or anything just a plain one pointing where your current location is so that when a new upgrade or a med kit appears you could reach it to pick it up to make killing more efficient. I think you get the picture.
I'm pointing this out because I had to run around looking for the upgrades all over the map whenever I heard the sound of a drop somewhere.
But after hitting the 90,000 mark it kinda started lagging or the performance dipped, not sure if it was because of my computer hardware or the game. It slowed down a bit for some time and then again got back and this kept repeating. I hope you check this out.
Finally when I die the game displays my current score as the high score when I played it for the first time, that is how it must work. But later when I played the second time and died my current score was displayed as the High score, meaning my previous High score of 140200 disappeared. I think that should be fixed, so that every user has a high score registered to their own accounts.
This game was well executed, in my opinion it could definitely do far better.
Really appreciate the amount of effort you put to make everything on your own.
Well done and Good Luck further !