I remember HATING this show when I was younger (I was about 17-20 while it was on the air), mostly because of the voice acting. It never seemed that amusing, and seemed like a bad use of a "Beavis & Butt-Head" character, and I LOVED B&B at the time. I just found the show annoying.
Retrospectively, it's quite good, and excellent at times. It REALLY captures the bleakness and annoyance of High School, and it can be pretty clever with the "outsiders looking in" and the quips and stuff. The animation & character designs also aren't that bad. But OH MY GOD THE VOICE ACTING. This may have the record for the MOST annoying voices on a single show. People often point out Daria's voice specifically, but at least she comes across like a real actor is reading the lines. In almost every other case, it comes across very poorly. Certain characters sound like they specifically told the person to act as annoying as humanly possible- specifically Brittany (who sounds less weird early on).
I love the episodes where Daria's forced to accept how her personality rubs others the wrong way, and how she deliberately keeps others at arm's length (basically criticizing her permanent cynicism). Ones where she argues with Jane are pretty good as well, or when she has to make nice with Quinn temporarily. Most of her scenes with Helen are excellent, and Helen's family is way-underused.
Another flaw is many of the side-characters: this would have been a perfect opportunity to develop Brittany or Kevin, but instead they're just doddering imbeciles. Though oddly, they don't go the tiresome route of having them be horrible jerks (there's some inklings early on, though)- Quinn & her group are Alpha Bitches instead. The dad's over-the-top antics feel like they come from a different series, though, and Trent is also very one-note most of the time (though an effective example of what many teen girls go for). Most of the teachers & parents are just one-note jokes as well- it seems like only the Core Cast got any kind of development.
It's much like "King of the Hill" in that most gags come from the characters, and the show is rather realistic and non-slapsticky. I appreciate that. At it's best, the show is VERY good, but it can be a bit dreary and one-note with many of the characters.