My main criticism of the game would be the boring level-design and lack of secrets. It feels like Metroid 1 in that regard, just randomly placed platforms to jump on,but no real coherence. I love how much variety there is in the levels themselves (graphics-wise) but again, all the levels feel the dame due to the design.
Compared to games like SotN, Super Metroid or Shadow Complex, there is a distinct lack of secrets in the game. You have no reason to search the levels for stuff because there isn't anything to find except for a few useless gems here and there. In Metroid every block could potentially hold an upgrade, here there's nothing of the sort, all you do is grind enemies for gems and buy upgrades. Which brings us to the back tracking: seriously overdone. You need to traverse a big part of the map to go past an obstacle only to get an upgrade you can use back on the other side of the map! This happens several times. Without any secrets to find in the meantime, back tracking becomes very tedious.
And my last part of criticism is the controls. They work fine, don't get me wrong, but when you're playing a game that so obviously wants to be like the aforementioned Metroid or SotN, you can;t help but compare the games and here is where the controls fail: no weight, no momentum. Henry Hatsworth had the same problem. In Super Metroid, everyone could play and finish the game, but to really master the controls took time and skill. Monster Tale controls just fine, but the second you play the game, you've mastered it, there is no nuance to it. Now this doesn't have to be such a bad thing and it might just be me being overly critical, but I never could shake the feeling there should have been more to it.
Now I've noticed myself latching on to the lesser aspects of games and harping on those instead of also mentioning what's good about a game (it's funner to bitch about something I guess) so let me just say this: I actually really like Monster Tale. The graphics are colorful and diverse as are the levels themselves: you never spend too much time in one place, you get a nice, steady flow of upgrades that progress the game, the difficulty ramps up nicely towards the end without ever being frustrating.
Money is actually useful in this game. You use it to get upgrades, but it's rare that you have enough cash to actually but everything you want, which makes seeking out money actually worth something. The music, especially its main theme is very nice, also quite diverse which is always a big plus in my book.
The combat works very well too, I love how the game forces you to use both the blaster and melee attacks in equal measure and how you really can't rely on just one or the other, you have to combine attacks regularly which results in a very nice overall combat flow.
If I seem overly critical, it's probably just my own problem. I can't help but compare a game similar to some of my favorite games (Super Metroid being probably my #1 or #2 game of all time). But grading the game on its own it really does do alot of thing right and if you're a fan of the genre I highly recommend checking it out.