I've been wanting to try it out sometime, too. According to the fans, the manga is far superior to the anime in terms of characters development.

I liked the part where they all went bowling.

Just kidding, I have no idea what it is.

I read the manga, and I'd sum it up as an interesting fusion of swords-and-sorcery RPG + magical girl + giant robots. The plot plays around with your expectations — the three girls are initially summoned to Generic Fantasy World in order to complete a standard "rescue the beautiful princess from the evil guy wearing black" quest, but once they get close to completing their mission, they discover that the true nature of their mission is very different from what they'd been told and completing it leaves them all feeling rather traumatized. Then in the second arc, they return to Generic Fantasy World and see the aftermath of their rescue mission — the world they "saved" is now falling into disrepair because of their actions, and now they have to help save it again.

I know the anime gives the heroine a Psycho Lesbian stalker rival, and I think it fleshes out the characters more due to its length, but it also lacks at least two plot points from the manga that in my opinion make the manga preferable.

I am fond of MKR. It's early Clamp and eraly-ish for it's type of Magical Girl plot (and it shows in both ways) and it's rather sparse, condensing a ton of plot and characters into 6 volumes of manga, but IMO, it's fun and pretty solid, and has lots of girls being BFF and having adventures.

I enjoyed the anime. I haven't read the manga yet.