I don't really think Planescape is as good as people remember. Maybe it was just my group back in the 90's, but it was a great example of a set that I *really* wanted to love (and did, on paper), but didn't really translate well to actual games. At least not for normal long-term games.
Planescape, to me, was like Ravenloft. It was a place you could bring into your existing setting for a good end-game or side quest type adventure, but neither really really great settings on their whole.
I actually find it to be much better than I remember it. My enjoyment of the Planescape setting really only came about during 3E when I started to incorporate elements of it into my campaign. Sigil is a great location, and that alone makes Planescape compelling. But it also made the planes more accesible, while simultaneously more mysterious and strange.
Neither I nor my gaming group really appreciated it back when it was released and we first played it. A big part of that is likely the fact that the person who was the primary DM for our Planescape campaign wasn't that strong of a DM, and the rest of us relied on him to kind of reveal the setting to us.
But over the years I picked up a lot of the old supplements about the planes, and the more I picked up, the more I found the material to be really strong. Especially the later stuff by the likes of Monte Cook and Wolfgang Baur.