For me it's an average game.
First, why bother with a mana system? The cooldown is enough to equilibrate the spells. Here, you just spam your frostbolt, use fear when there are some healers and when you have no more mana you're basically dead. The core of the game is spamming the forstbolt as fast as you can but you're doomed from the start because you use your mana faster than it regen (in survival mode of course).
There is plenty of things in the game, but too few of each.
-You have units, but you can't command them or really upgrade them.
-You have traps, but only 2 differents kinds and nearly no upgrade.
-You have spells, again very few power-ups and some are too weak in respect of the cost of skulls/mana
In the end, you have some good ideas, but none of them is fully exploited. Meaby the "arena" is too close so you don't have the room to add more stuff...