I am a big fan of this game but I think its way too long considering all the replaying you have to do. The length of the first one was ideal in my opinion. I got bored with this one way before the end.
Its kind of foolish that if you die and press continue you lose all your cash. Then you end up stuck on a level with a crappy gun and no way of ever beating it and you have to start over. I tried playing with a challenge by going as far as I could with a pistol and saving up. Then I died 1k cash short of a gatling gun and that was pretty much game over. Not too good.
The balance is a bit off in this game. Buying shotguns and machine guns will get you an easy win. The larger more expensive guns are just a waste of money.
The hit detection did it for me. I'd probably give this game a 4 or a 5 if you could move a little more quickly and be a bit more agile but many times i found myself dead by a block that had just recently disappeared or by the game thinking i hit something while my character was only close to hitting. Takes away a lot of the fun with that frustration factor.