Infuriating
The monetary issues have already been touched on, but overall the game just screws over the player too often.
I put about 2 hours in, got a creature to about level 300 and decided I wanted to "fuse" him with another rat for a second time so i could finish up the game. My first fusion was a total waste (had no idea each fusion would reduce the chances of it taking). Well this second time i figured i'd be a little wiser and actually use a high level rat, i was pretty pissed I'd thrown the first one away because i didn't know fusing had permanent bad effects. So i saved my game, tried another fuse at 70% chance and it failed, Reduced my creature to level 170. No big deal, i'll just reload. Reloaded and I was at 170 still. What a joke.
Other than the grief the game has some interesting elements, i like the idea of experimenting on the rat, but since a level is a level, rather than certain experiments enhancing specific properties of hte rat, you just end up going with what works best.
Best strat i found was to just irradiate the CRAP out of my rat and keep him alive with endorphines. 10 mins go by and you're up 100 levels, just takes a bit of money to buy the endorphins and pay for the revival of the rat. (this is also a bit buggy as the stats can go over 100%)