It's a fun, simple shooter that becomes quite relaxing once you get about 1,000 or so points, and then it's more about how long you feel like playing because the challenge is gone and you're instantly pulping almost everything on screen- I got to 5,000 and then decided that was enough- so I'm sure my world record will be broken before too long.
Also, I reached a level with two of the weapons where it said 'undefined' and I couldn't click on them. Not sure if this is a bug or feature? But, yeah, good game, and always plenty of additions you can make to a game like this.