Linux steam performance

Ill start this straight, since i migrated to Ubuntu i haven't used it for gaming, but now i noticed something a bit off, I thought that, since my desktop is a lot lighter than Unity or GNOME i would not have any issues while gaming some low spec games like Half Life 2 or so, but it seems that even those lag now on Ubuntu MATE, is there a way to increase performance so they run smoothly again? i dont waa have a windows machine just for gaming.