I think the cartoon is genuinely very good, and I enjoy watching it every now and then.
The special itself though, is so bad it's... bad. It's TOO bad to be "so bad it's good." I sat down to watch the whole thing a few years ago, and actually had to quit with about 15 minutes left, I just couldn't take it. I can't enjoy it ironically, or on any level (except the cartoon).
A few months ago I sat down to watch it with Rifftrax, but could only stomach the first 10 min or so.