Photoshop :: CS5 / Unable To Use Brush Feature For Entire Duration?

I've been using Ps CS5 with a wacom graphics tablet on my mac for over a year now, and have been unable to use the brush feature for the entire duration. With or without the graphics tablet, brush strokes come out as pixelated. I've gotten around that by using the mixer brush instead, which doesn't come out pixelated. However, that's pretty limiting.
 
I've trained on Ps with a graphics tablet on other computers prior to owning it without this problem and researched on forums to no avail. I've reinstalled both the tablet and Ps and had no luck.