This is a really cool concept !
A bit confusing at first but, once you understand what's going on, there is actually quite a bit of strategy & cool tricks to learn in there to get your opponent where you want him to be.
The controls are a bit frustrating. as it require to be precise with teh mouse in a really fast paced game. You could have taken adventage of the mouse a little by binding the actions directly on the mouse buttons as there is basically only 3 actions (switch portals, shoot, brake).
Shooting with the left click, breaking with the right click & switching portals with the scroll wheel would have made the whole thing a lot more enjoyable & easier to handle, as it allow you to keep yours eyes on what comes next instead of constantly checking if you're clicking the right buttton.
All in all, It's a really really fun & enjoyable game & with different controls I could easily see myself spend quite some time trying to beat it.
Good job :)