It's a great execution on the horde mode genre.
Few points of feedback.
- So far, the elements don't really have any crucial differences. Cold has high range aoe, ranged attacks, low range aoe. Lightning has high range aoe, low range aoe and so on.
I'd like to see larger pros and cons for picking a particular element over another.
Same with the additional effects each element provides. Ignite, Bleed and Shock are essentially the same effect in a different costume. - Some of the gameplay elements could use cleaning up. At one point it becomes nigh impossible to differentiate between projectiles, xp orbs, player's abilities and enemies. Perhaps stronger color-coding could be used to improve this.
- More abilities. So far there aren't that many different skills and those that are here, as mentioned before, are very similar to each other. More variety. Perhaps using the carving system, one could add/remove various effects from skills themselves. For instance, place fiery rune on cursor, but it explodes after 3 seconds and so on.
Overall, this is a great start. Keep at it!