This was not only one of the best episodes of Angel, but simply one of the funniest things Joss Whedon ever did (and that says a lot considering Whedon's consistent, naturally uproarious sense of humor). I think they key to the episode, from Whedon's perspective, was to give Angel fans a reminder of who these guys and gals were. At the time Whedon was working on Firefly, so his writing/directing gig on Angel in season four was very limited, so coming on to it during a very dramatic time (Angel/Connor problems, Wesley still unsure of his future as a rogue in relation to Angel or Lila, impending Armageddon by the return of Cordelia) was a special case. At the start of this episode it seems very tense between Wesley, Gunn and Fred. But by giving the whole 'bottle' twist being everyone losing their memory back to before everyone knew everyone else, it adds a great sense of comic irony to the proceedings.
What drives the episode so wonderfully is the dialog and the performances, how the actors show their range past their usual selves (Boreanaz especially makes Angel, aka Liam, into a really wimpy character who constantly hates on the English, i.e. Wesley), and have to face the challenge of what's around them- like an AH DEMON! in Lorne- and themselves really. Whedon gives everyone a chance to shine, and it works completely. In a sense it's a little like a repeat of the episode from Buffy in season 6 when at the height of drama, just before Giles leaves for England, the characters' minds are wiped. Only this time, there's a lot more humor, naturally coming out of reactions and how we already see these characters (Wesley doing his vampire-hunting moves is a riot), and the framework of Lorne doing a one-man-show explaining everything (kind of like in Bob Fosses' Lenny).
I'm not sure if it's quite as daring as Whedon's stand-alone episodes at his best (then again, what can top Hush, Restless and The Body), but if you're looking for the sensibility of humor that Angel can excel at (quips and sarcasm and in-jokes, not to mention cultural hoots), then it's a must-see.
