There's a lot to like about this game. Certainly brought back memories of retro style shooters found on random websites when I was at school supposedly doing research.
There's a completely over-the-top, zany plot, loads of weapons to pick up and try out, tonnes of unique enemies all with their own weapons and skills, bosses who really refuse to give up and plenty of infuriation.
The only thing I would say is that the gap between easy and normal mode is a bit large (easy mode gives you 10 attempts per level, normal mode 2), but other than that this is a solid side-scrolling shoot-em-up with a lot of replay value, especially with the randomization of the levels and power-ups you can get.
Well worth your time, I'd say, just don't come crying / screaming at me when you die for the millionth time!