Where do I begin? I guess I'll go from the reverse, but have to say to anyone that reads this that there are SPOILERS INVOLVED. ***Ok after level 8 you don't need to upgrade the health anymore just get more bullets. The last stage is fun, and you just need to keep shooting to avoid getting shot and to destroy the car.
You don't need to ugprade laser damage because there's only a few spots they come from and if you know how to shoot you won't need it, otherwise you can just switch it on and off as you aim. Definitely focus on health upgrades in the first 3 rounds but have at least 3 bullet upgrades from levels 4-6 and then give yourself more health. It doesn't get challenging until level 3/4. That's it for spoilers
I love the way you have to use the mouse to reload, that's very interesting, I don't like all keyboard games. I beat the game pretty fast but I did die twice, I have to say if I played it again I wouldn't die one time. I would love to see a sequel with perhaps a storyline involved and perhaps some choosing of where it leads.