This episode, while I do not think it was the best episode of Frasier, was definitely one of the most memorable.
The one thing that truly made this episode shine was the progression of the characters. Martin's marriage, Daphne and Niles' child and Roz's new job showed just how much these characters' lives have been affected (positively, of course) by Frasier. Niles would never have met Daphne, Martin would never have met Ronnie, and they would never have been as happy as they are now. Also, his goodbyes to the family, where each character tries to be the person they were in the first few series (Martin's awkward jokes, Niles' stiff handshake and Roz's quick acceptance of the facts) while their true feelings are clearly breaking out is truly heart-warming. In particular, the tears in Martin's eyes as he says goodbye to the son who has loved and cared for him for eleven years, as opposed to his original gruffness brought tears to my eyes, along with Niles' final line 'I'll miss the coffees'.
Indeed, I will always remember this episode as the one where everything and everyone turned out fine, because of Frasier.