Now that I finally have my computer back, I can actually talk about this game!
I played the 360 version and enjoyed it quite a bit, but I had a few issues. First of all, the text is almost completely fucking unreadable on a SDTV. I'm going to save my second go-through to get the achievements I missed until after I get home and I can play on my nice TV. Secondly, although I liked the game and I will buy the next one even at the same price, 20 dollars is a little steep, both by standards of episodic content (Sam and Max episodes are significantly less than that), and on XBLA, where it is the only game to ever cost that much. Only a couple had even cost 15.
That being said, the comparison to Mario RPG is totally accurate, and most of all it just feels like a Penny Arcade game. The writing is 100% Tycho (which makes sense, since he did write it all), and the art team did a reasonably good job of bringing Gabe's style into 3D. There were a few moments in the game where I actually laughed out loud (the sidequest that gets you the health upgrade was my favorite moment, and I won't spoil it for anyone). The trial doesn't really do the humor of the game justice, in my opinion, because you don't get Gabe and Tycho in your party until the end of the demo, and like the comic, a lot of the humor comes from the clash of their personalities. However, I think they did a good job in not making the game too exclusionary for people who don't read the comic. Gabe and Tycho are consistent with their comic personalities, but aside from Anne, none of the other characters are even from the comic.
Basically, if you like Penny Arcade, get it. If you like old school RPGs and aren't familiar with Penny Arcade somehow, try the demo but be aware that it gets much funnier later on. If you don't like Penny Arcade, well, you probably weren't considering it in the first place.