When you're puffing like your on top of Mt Everest, You've found the right routine...
Nothing will wear your ass out like legs...
Squats are the main course. Learn to do them right.
Start LIGHTER so you can go all the way to the floor and back up for a Rep. Get into that habit and work your way up with the weight.
Nothin is funnier that seeing guys load up a bar with 300 lbs in the squat rack, then only going down 2-3 inches and feeling bad-ass.
As a leg day desert, I just added heavy DB lunges. Sweet!!!