We just returned from 4 nights at HRH. The character meal there is at the Sunset Grill on Saturday nights and the characters are Scooby Doo and Woody Woodpecker. We didn't do the character meal because we wanted to do the Mardi Gras parade on Saturday night. But we did eat at the Sunset Grill on Friday night, when they had a magician that went table to table performing. We really enjoyed the magician, but except for the 6 yr old in our party who just got a kids pizza, the rest of us were disappointed in our meals. Three of us ordered hamburgers, cooked medium. When they arrived, the meat was burned to a crisp on the outside and dripping blood on the inside. My sister's was so rare that the bun was soaked red. The manager gave us complimentary deserts, some of us got chocolate cake and some got strawberry shortcake. They were all so dry and bland that none of us finished them. The total bill for the 6 of us was $143 and that was with the free deserts.
I would recommend skipping the character meal at HRH. The characters were out in full force in the parks the entire time we were there. We saw Woody and Scooby, along with Shaggy and the Mystery Machine repeatedly. And it is not difficult to get to them for autographs and pictures.
If you do want to eat at Sunset Grill, I don't think you need to be too concerned with getting advance reservations. The hotel was completely sold out both Friday and Saturday night, but the Sunset never looked like it was busy. I would say on the Friday we were there, there may have been people at a quarter of the tables. That was at 8:15pm.