Having watched most of the top 100 of AniDB/ANN, I'd say they're pretty good. It really depends on how wide a range of taste you have. It's also obvious that, as someone mentioned, newer hyped series are way overrated, as well as sequels sometimes (probably because the people who bothered to watch the sequel are the type to like it). Anyways, after seeing most of the top end of the lists I just use ratings as a lower limit and watch what appeals to me, which mostly ends up being romances, comedies and scifi minus mecha.
Hopefully anime-planet's ratings system will come around soon as AP is easier to use than ANN and far easier than AniDB. You might want AP's recommendation system too (although I've seen some really dumb recommendations and there's no apparent way to vote them down).