i got introduced to friends through the dvd box sets, and it's been a pleasure to watch them in order, with the full episode included, uncut. certain lines or parts of scenes are cut out on tv, so if you're a die-hard fan, having the episodes on dvd can be preferable.
i'm liking the third season better than second right now, but that's only a personal preference. there are some classic episodes included on this set - lots of ross and rachel, joey's first big role as drake ramoray on days of our lives, joey moving out of the apartment with chandler, and monica's relationship with an older man, richard. being that chandler and phoebe are my favorite characters, i missed their involvement a bit, but they got subplots.
highlights: ross and rachel 'you-knowing' in the planetarium part of the museum where ross works, phoebe's "smelly cat", ross making a list about rachel, monica's character developing as she grows closer to richard, chandler finding an internet girl who turns out to be janice, all the tension between ross rachel and julie, etc.
lowlights: something about the episodes where eddie moved in seemed less well written and a little tedious. maybe it was just the fact that i was sick when I was watching them. *g* the fact that there are no chapters in episodes themselves, as others have mentioned, is a drawback. should have commentary from the six main character actors themselves; other shows do! deleted scenes would be nice; some of the special features seem useless, like showing a short clip of each guest actor when if you just watch the episodes, you have the whole thing. being able to check out monica and rachel's apartment in detail was kind of cool, though. and the quiz game was fun. if you get it wrong, it shows a clip of one of the characters shouting "no!", which i thought was incredibly clever and funny.
that's all i can think of off the top of my head; i'm at work and can't check the dvds for specifics. :)