This is a really great game you've made. It's really not too hard but neither is it easy. This game's a fantastic way to kill some time and that's everything I need from a game.
In the last note of the developer i think it became pretty obvious that he just abandoned the game and there will be no more updates for this game. The other thing is that he's not even reading the feedbacks. Nothing proves that better than his last note. If this is his way to develop a game i think i don't want any other games from him.
There is another bug or glitch (actually i don't know what it is) in the achievements system because in the statisticts shows me that i have 53/48 achievements but i couted them and i have only 43/48
You are complaining about that you can't level up at level 90 or 100. But what can i say at level 138 and what can say someone who's level is above mine?
You should work on the mystery upgrades too because on higher level they aren't mysteries anymore. They gives the same things every time. You should do something like multiplying them after every 5th level.