It's obvious that Konami didn't give MS a big enough budget to allow for fully rendered cinema scenes, but in doing so they were able to dedicate more time to the gameplay, and it shows. Sure, they crammed a lot of puzzle in there to extend the playing time, but with the exception of that tedious buzzsaw section, they were quite enjoyable for the most part.
The two main criticisms I've seen of Reverie are that it is too short (which is well warranted) and the direction of the storyline. Unfortunately, due to the way the DLC was advertised, I think way too many people got their hopes up. The trailer for Reverie made it very clear that Laura was the one who turned Gabriel into a vampire. Cox gives away far too many details about the story. LoS's ending/plot twist was strongly hinted at throughout the entire course of the game. Also, the "Back to the Future" reference in the Founder's Quarters level was cheesy and unnecessary.
I felt that Robert Carlyle did a vastly better job narrating the opening of each level than Patrick Stewart. They probably went with Stewart for the main game due to name recognition, but it would have been interesting to see Gabriel's "descent into darkness" through his own words.
For those who feel that this is a retarded way to explain Dracula's origins, answer this: Were the previous explanations really any better? In CV3, the completely ambiguous "Poltergiest King" gives Trevor Belmont the Vampire Killer whip to prevent Dracula from "practicing sorcery to create a bad world filled with evil." :

Legend's story was/is almost universally hated, and LoI? Just some guy renouncing his faith because his wife died, then duping his best friend into killing a powerful vampire so that he could claim his powers. Sorry guys, but Castlevania has never been known for its brilliant storytelling.
Call LoS's version of the story ridiculous all you want, but in the context of character development, few games can match it.
Overall, it was quite good, but not long enough to justify spending $10. However, I can totally see Konami pulling some kind of bullshit that requires Reverie to be purchased in order for Resurrection to become available.