I think it was good that there wasn't too much building up to Phoebe's wedding. There has been so many weddings over the series and so many episodes related to that that I'm not sure whether it would've been very interesting anymore.
Anyway, also I find that Rachel/Chandler relationship annoying.
For some reason the fact that Joey clearly wears underwear in TOW Al Pacino's Butt (you can see it on the shadow) annoys me every time I watch that episode. I don't know why, I don't even normally get annoyed with small mistakes like that easily.
There has been also some other, mainly continuity stuff, which has bothered me but I only tend to remember them when watching.