Very cool game! It was one of the games that I really wanted to replay again, but I totally forgot about it, so I'm kind off late, but still, glad that I played it again. The story is kind off basic and a bit too generic, but that's not a big problem. I really loved the level design, all the different weapon types that you could get and especially the Area Challenges. They were quite unique, it wasn't just a "kill ... enemies" or "collect ...", it had some pretty interesting missions in it, such as bringing the chickens into one place or extinguishing the fire with the squirt gun, was quite a neat touch and gave us a small break from all this pure action madness.
The combat system was a bit too simple and repetitive, but the different weapon types, as I've already mentioned, made the gameplay still amazing. I also think that there should be more upgrades, such as health, armor, lives or something like that. Sad it didn't have any NG medals in it tho
Anyways, great job on this game! I'm excited to replay the sequel, too :P