RHOD is probably WotC's iconic moment in 3rd edition; when it came out, several people hailed it as being an instant classic on par with Temple of Elemental Evil for enduring quality and generally setting the standard. (Some people would argue that Paizo's adventure paths in Dungeon magazine beat it, particularly "Age of Worms" -- I won't get into that here. "AoW" does look very cool -- unfortunately, as it'll never see hardcover compilation, it's sort of an apples/oranges comparison. But I digress.)
RHOD has a structure similar to Icewind Dale II, for those who've played that -- an army of evil humanoids is descending upon civilized lands and it's up to the heroes to turn the tide. The cover says it's intended to take characters from levels 6-12; the inside says levels 5-10. Which one is correct? Hard to say. We only got through the introductory teaser fight last night, and that was a pretty hefty slog for a party of five 6th-level characters. Granted, there's a lot of multiclassing and LA going on, so the party is not the most optimized you'll come across, but they're no pushovers.
Right now there's not a lot of characterization or group dynamic going on ... in order to get right into the action I just said, "You guys have been adventuring together for a while and you've got a treasure map. Go!" Who the characters are and how they relate is yet to be determined. There is no "GM's PC" right now, and I don't know if one will turn up. There is a tag-along NPC in the adventure who may or may not join up depending on how things go, but without wanting to give too much in the way of spoilers, his skillset would be a bit redundant with the group as it exists right now. If this group does have a weak spot, I'd say it was lacking in either a dedicated cleric, or a dedicated rogue. A scout might work, tho. Maybe I'll send them a Celedras-variant for support if they need it.