I like how you spliced the idea of a standard shooter with the talent point system for upgrades. It really reminds me of the system used in MMOs like WoW, so that part of it was easy to figure out, and actually refreshing to see in a shooter. Also, as much as everyone's griping about the level cap, I think it's actually perfect as-is, since it forces the player to choose a strategy for building their passive talents. I'm also pleased with how each elemental tree focuses on a different sort of play style. However, I do think there's some balance issues due to the way some spells work.
Fire appears to be the strongest tree, and yet neither spell in that tree is really worth taking. It's all about having the biggest, baddest fireball imaginable. I found myself sticking to the default spell arrangement and leveling Divine with it to get the highest possible spell damage, although one could probably try going Ice to gain additional damage from Frostbite and faster casts through Master of Cold.
Ice, while not as good as Fire, seems to be pretty solid as well. It appears to be the "rapid fire" set, increasing the player's DPS not through added damage, but increasing the rate at which damage is caused. Icebolt works very well as the spam spell, since it makes up for the loss in spread by including a slowing effect and monstrously fast recast time. I popped Swift Retribution onto my Ice build to further enhance his Icebolt recast, as well as Hot Air for the move speed, so I'm pretty sure he's the fastest caster and best at avoiding attacks as well. Judgment probably would be great fro this build too.
Divine, IMO, is the weakest of the trees. Its spam spell, Smite, doesn't have any splash like Fireball and Icebolt do, so you pretty much have to have one or the other casting simultaneously. The fact that enhancing Divine's damage by improving crit rates to astronomical levels doesn't sit well with me; it feels less like you're increasing your chances to do double damage with your spells and more like you're reducing your chances of doing half damage with them. Also, even talented, Judgment doesn't cast fast enough and costs too much to be an effective spam, and Spark of Life also is too costly to be of much use. I'm probably playing it wrong, as I tend to take a more aggressive approach to weapons choice when playing shooters, so Divine may be much more effective in the hands of someone used to playing defensively, but for me, it was the weakest.
While there are definite issues with balance between the trees, I have to say this is a great game with an awesome concept. I'd love to see it developed further in the future. For example, perhaps add on other types of mages that have unique trees, like Shadow or Lightning to replace other trees in the Wizard class's set of Fire/Ice/Divine).