Dester666 is partially right, but also wrong in MY OPINION. The level up stats are kind of useless late in the game, like most magic spells. When you just start, leveling up stats and magic spells are essential if you want to progress quickly. I still think Frozen is really good, it lets me click worry free. Enchant weapon is needed with Frozen though. Without the enchant, frozen is not worth the mouse clicks. Lightning bolt and meteor are too much alike. I feel the need for only one of them. Right now with ~7000 magic, lightning levels me up (100%-0% mana) about 3/4 of the way. Meteor levels me up almost a full 100% but you don't get the gold. Pretty similar IMO. That's all I have to say. However, I currently like the game where it is and I don't think it needs changing yet.
Some ideas for the game:
1. Achievements
2. Boss fights (Every few rat kills [will increase with level ups] you will get the option to fight a boss, deal enough damage in a set time and you get some loot, gold, and experience.
3. More variety in the items. What you have right now is some pretty standard stuff. It needs more rarities (common, rare, epic, legendary)
4. Able to press 1-4 to activate the spells (I thought about this one for a while. I'm not sure if it would be good or bad, seeing as this is a mouse only game.)
5. Maybe something more to do with gold, but I can't think of anything :P
This game has some real potential. I look forward to seeing how well it turns out with future updates.
The game was really fun for the first little while (Currently level 411, 581 Attack, 828 Defense, 542 magic), however... the fun dropped fast. It needs something to pull me into playing it.
This game would be much better with a goal. Maybe achievements or progression through bosses. Something along those lines.
That is all I have to say for now, but i'll repeat again. I really REALLY look forward to seeing updates on this game! :)
I'll follow up with another comment explaining some ideas I thought about. I would write them in this comment, but apparently there is a maximum character length.
Crafting, legendary items and demonic items (crafted) coming in 1.3. Crafting the whole set of demonic items will be a great goal. More goals coming in next patches (uber rats, the rat king :) )
Follow fb.com/ratclicker to get more info
 "Rat Clicker"){kind=icon}
Thanks for feedback!