Almost there
I'm playing this game for more than two months now, so it's not that boring...
Actually, I can follow quite some of the remarks about the difficulty and the "boringness" : the game is so complex it takes a while to get into it. First thing is to get all the different gems and combinations. You really have to get used to it, know exactly what is which, which enemies react on which gems and so on. If you're not aware of that, you anticipate the game as being "create as many gems, place them in towers and hope they kill everything".
Then you discover this game is soooo much more. Honestly, it's only after I started paying attention to the colors of the gems , got the details of the mana system and discovered the bombs, that I really got into the game. Beating it requires quite some strategy, and that is a good thing!
A big discovery was the "speed up" : if you let the waves come faster, you don't only gain more mana, you get more points which gives you upgrades faster. By using the upgrades wisely, you can get very far without much trouble. To get the maximum out of the upgrades, it's a very good idea to get as many "glowing frame" scores as possible. This is done -again- by letting the waves come faster, and by building towers, making gems, throwing bombs : the more of that you do, the more points you get as well.
The game itself is flawless, I didn't find anything wrong. It's hard, but far from impossible. By now, I'm at level 55 and I cleared most of the map. The difficulty is set right I believe : challenging enough to keep you busy and attentive, but not so hard that it's impossible to beat. The only level I really don't manage is the first hidden one, where you have only the poison available. The last boss always kills me.
The game is also very nicely executed, with good graphics and a fitting sound. All together makes this game a top game.
A full ten, keep them coming.