To be honest, I never found any of the main six anoying - I liked all of them. There were some "guests" I found anoying though (Emily, one of Ross' girlfriends springs instantly to mind here).

I think the humor pretty much worked throughout the series and the show worked better as a sitcom rather than a comedy (yes, there is a difference) it humanized the characters enough. The only drawback (and a minor one at that) is that I can't really find enough differences per-series to sepperate them enough so, if I was to judge Friends as a programme, I would have to judge the whole thing as apposes to per-series/season.


Note: Having seen the whole show, I really like watching the older episodes and seeing the Chandler/Monica scenes - it's almost like it's foreshadowing sometimes, it's kinda cool.