I don't normally post on the GR forums, but I shall start doing right.. now!
As subcalvin and TheBigTW pointed out - On the Rain-Slick Precipice of Darkness is in my opinion, definately for fans of Penny Arcade. I'm sure non-fans can play and enjoy the game also but they probably won't be into as much as a fan.
The writing and dialog is brilliant and is hilarious a lot of the time, very random. Despite being set in 1922, they talk like they do in the comics, using modern language ("You motherfucker") etc.
The graphics aren't the best, but the cel shading works regardless, really gets into the actual art style of Mike Krahulik (Gabe). The 2D cut scenes work too, and are quite funny, but as my friend pointed out as we played together, "It looks like it was done in Flash."
The sound track is.. no exhaggeration here but absolutely stunning. It's just, so I don't know, epic. It's like the music is from a Tim Burton movie, very dramatic orchestra.
The character creation system could use some work, there's not enough options in my opinion. But, to be absolutely fair, whatever character you make will look like the character you've made in the animated cut scenes, which is quite cool, so I suppose there's a reason why the character creation may be limited.
The game play is pretty simple. Outside of combat (for PC I mean) you just.. click on where you want to go, and you move that way. Like Diablo, in a way.
Actual combat is simple, yet effective. It's turn based combat, except every character on the screen has a cool down time on each of their stuff, use item comes first, followed by basic attack, followed by special attack, once you bust something out, your entire selection (items, attacks, special attacks) returns to zero cool down, and you've gotta wait again to do an action. You can also do special "team up" attacks where two, or three (all) characters attack the one enemy at once for "MASSIVE DAMAGE".
The special attacks are quite cool and in a way, somewhat "interactive'. For example, with Tycho, when you bust out a special attack, you'll see a picture appear on screen with a letter/direction indication, telling you what to press. For example it might say "W" - thus you press either W, or up. You keep doing this (more directions/letters will flow) without losing time, and you can bust out maximum damage on your special attack.
If an enemy attacks you, it is possible to block, and even counter attacks by tapping the space bar button at the appropriate time (when the enemies' health bar flashes white).
[Edit/Update] You can also acquire new weapons via weapon upgrades. Unfortunately, you can only acquire up to two further upgrades (three upgrades overall).
I think my biggest complaint however, is that the game is too short. My friend reckons he read up on the 'net that to play through the game normally without collecting everything is like, six hours. To play through it while collecting all necessary stuff is probably eight hours, and to play through the entire thing collecting absolutely everything (concept art, music etc) is probably ten hours. I finished the game in about eight, myself.
Sometimes, the enemies are too easy to fight. You'll be fighting new enemies and may be having difficulty countering them, but once you've got it, you can mow 'em down pretty easy. So sometimes, the game feels a bit easy.
[Edit/Update] Regarding special attacks, I wish there was more variety. You only get up to three maximum, which is a shame but, hopefully we'll see more in Episode Two.
I can't wait for Episode Two though, I'm definately gonna grab that. If you're a fan of Penny Arcade, I highly recommend you check the game out. If you're into RPGs and comedy, it might be worth having a look at.
If I could give the game a GR style "score", it'd probably be either a B or a B+.