Personally, I don't think so at all. The S season especially is among some of my favorite anime of all time (and I've seen many), I personally rank Sailor Moon up there with such greats as Evangelion and Cowboy Bebop. It does have some noticeable flaws -- some cliche character and story concepts, a lot of filler, a lackluster season (SuperS), etc. -- but the show has enough truly outstanding moments to make up for all that. Some of the common complaints, such as the filler, don't even bother me that much -- I actually think most of the filler is good and help to add humor and character development to the show.
I have noticed sometimes it's common for people to rag on it, though, and compare it negatively to more renowned series. To each their own, I suppose -- also to be fair, a lot of them have probably only been exposed to the DiC dub, which is a lot worse than the original Japanese series imo.
There is one flaw that gets to me more than the rest, though... and that it gets really hard to suspend disbelief sometimes when it comes to the "secret identities" story arcs -- the fact that the characters look near identical in both civilian and Senshi form and yet we're supposed to believe they don't even suspect a thing. It's one of the few things that really detracts from the quality and emotion of the storytelling sometimes and reminds you that it is a kid's show -- it's still a great show regardless, don't get me wrong.