I can't say it's a terrible game, because I've spent the 15-16 hours required to beat it, but it's certainly nothing special. I don't know who thought the idea of "mouse buttons move unless you click a target and then they attack" was a good idea, but every game I've played just shows it's awkward. It's only saved by the reflection system and the ability to abuse the hell out of the very basic game play mechanics (rewarding in its own way).
As to the actual scripting, the voice acting is good, and Deathspank himself is of course hammy, over-the-top and very entertaining. Good, silly dialogue.
You can really tell it was never meant for PC by the layout and style. Still, if you're looking for something funny but mindless you could do much worse.