Portal Pro is a set of test chambers focusing on solving puzzles locally rather than using complex fling techniques. The goal here is that the solutions are hard to come up with but easy to actually do.
I love this mod. This is my absolute favorite mod. The only thing about this mod that isn't perfect is the replay ability because when ever I play this, I already know all of the solutions, thus making the mod WAY easier than it was when I first played through it. This is the best mod ever. Nothing can possibly be better than this. If I could, I'd rate it 20/10 Hehe.