This game has pretty fun system! Although, I was at first confused at the difference between mana generation and amount, and between the LMB and RMB attacks, but I got used to it! I think one thing that would make this game a lot more fun would be different enemy types, or ways to gather solar energy! Like an enemy that drops energy, or maybe different stats.
One small thing is I think you swapped the normal and special attacks though since the description says RMB for a special AOE attack but LMB does the "big arc" projectile with half as cost as the other one. One term you could change would be "spell cost" which at a glance, I was thinking "Hmm, why would I want to increase my spell cost?" so just a slight tweak there.
The graphic style is pretty good, and cohesive. The gameplay does feel a little slow at the start due to the player's movement speed but does get hectic over time.