From looking things up on Wiki (had to remember how to spell a few names and stuff), I got the impression of what Jerec said. The first two are Live Arcade games that are $10 or so, I think. Since I never got into the comic or other PA stuff, I ignored them and only bought this one because Zeboyd made it and, from what I read, they completely adjusted things to fit their style.
So it's kind of on this island where I loved the game, but still have no desire to play the first two due to the whole "different company" thing. Although, I do want to play the DeathSpank games at some time, but that's more because I've read some good reviews of them that make them look like the kind of thing I'd like. Point-n-click adventures have never been my thing, for whatever reason.
I'm not afraid to die because I am invincible
Viva la muerte, that's my goddamn principle