Very good if you are just starting out! It does have a bit of charm, and quite a lot of content to it. I managed to beat all of the standard with most badges, and a decent bit of the bonus levels with all badges before writing this.
This game has a few things that could use improvement or polish. The biggest issue I noticed is the movement system; it didn't seem quite so 'spot on' to me, it seemed instead rather sloppy. For example, it employs both acceleration and momentum, which isn't necessarily a bad combo for a precision platformer, but when combined with low deceleration values, and the air decel value being so close to the ground friction, the controls feel really slippery.
Long jumps with a full running start seem to require just as much time to stop as they did to build speed, which tends to obviate precision placement, as the player needs 'runway' to slow down after they land on their platform. Since there are many levels with small platforms, these quickly become tedious, feeling more like work than play.
Additionally, there are other movement oddities that make movement difficult to predict (in addition to being slippery). For example, landing on a platform with no key pressed instantly cancels momentum, but if a key is pressed, the character must first decelerate his momentum before moving. This is the same when running - if you run forwards, then press backwards, you will continue to slide forward for a bit. If you release the key, you will simply stop. Up and Down instantly cancel momentum, unless you are in the air. Or, if you walk off of a platform then 'water jump', you will jump to full height, whereas if you jump first, the 'water jump' is only half height.
The final thing I would like to mention is that the enemies hitbox is bigger than their visual representation (either that, or the player hurtbox is bigger than his ground collision box). Normally, this would be fine and a good player in a game with good controls may never notice, but this just frustrates this game all that much more.
Fortunately, the content (AKA all of the hard work) of this game is very good! I enjoyed it enough to complete the main campaign with most badges. Fixing the controls would be an excellent step towards putting the bow on this, methinks. That, and another song or two, as the same tune gets old 40 or so minutes in (not to mention listening to it the whole time I wrote this review). ;)
Other ancillary suggestions/thoughts:
-Though you made excellent use of the enemies currently present, I was disappointed that the most challenging enemy is the one who moves towards you ;( Maybe consider more challenging enemies in lieu of loads of ultra-easy enemies in the later levels?
-This is very minor, but the water's size does not line up with the gun/player's collision box when in a wall. For example, though you can press against a wall and shoot water up with no problem, shooting water downwards will cause it to disappear into the wall. Obviously this is not an issue until the later challenge levels (when you are water-jumping because you want to shoot water downwards).
-It looks like you collision check for enemies before checking the wall. This is also minor, but it allows savvy players like myself to shoot certain enemies through the floors and walls if they are close to the edges ;)
Hopefully these tips will be useful to you sir! The game content is good, but the controls are really bad, even though the concepts you were shooting for are good (momentum, with shooting water modifying momentum). I hope you will make an update with tighter controls, I would love to play it!