LogFAQs > #966018755

He clearly doesn't suck (and remember in Episode 5. He didn't even need his lightsaber to stop Reva. Which was badass).
But he lets his emotions get in the way a lot of the time (as seen in the flashback fighting scene with Obiwan).
Fighting his old master, you can see the conflict within him. Deep down, he actually still cares for Obi-Wan, but he pushes on and lets his anger take over.

It's actually really interesting. When his mask breaks open in the finale, they use the red and blue of the saber colours across his face to show this conflict within him (red eventually consuming his face).