Hiya!
How do you feel about Sigil? Have you DM'd a game that featured it, or been a player in a game where Sigil was featured?
Well, like virtually all other things 2e... "Cool idea... but they did it wrong".
That was me and my entire groups experience with 2e when we played it (for about 3 years total I'd guess...2 consistently, 1 year here and there). Kits? "Cool idea...but...". Assassins being 'any class'? "Cool idea...but...". Customizing character classes or races? "Cool idea...but...". Etc. Sigil/Planescape fell into the "Cool idea...but..." category.
I think it would be like Star Wars trying to give a physical, medical, biological reason to the Force... "Cool idea...but...".

If Star Wars would have made it work from the standpoint of "The Force is a mystical energy force that binds the universe together"...and then said "People who are more sensitive to the force have increased midichlorian counts. A midichlorian is a specific protein that gets formed in and around various cells, especially myelin. One can learn to control the 'flow' of the Force in them...like learning meditation to lower blood pressure. The better you get, the more Force Control you have". That would be almost acceptable. But they didn't. They just plopped in this big 'explanation', "Oh, this person has a high midichlorian count...they'd be a powerful Jedi!", leading to the inevitable conclusion of: "Well, why don't we just cultivate midichlorians and inject them into people to turn them into Force Wielders?"
Sigil...same sort of thing. "Lets just take this decades-long metephysical model and just pretend that Sigil has always been here but nobody ever mentioned it before. Ever. Because...reasons.
Oh, and the Lady of Pain bothered me. I
hated the idea of some 'singularly omnipotent deity that was even more tougher than the other gods'. That, to me, reeked of "1-Up'ism". Min/Max. Munchkinism. "Yeah? Well MY character has a 26 Strength! THAT's how strong he is!".
groan My work around was simple; all the gods/demon lords/arch-devils each get a seemingly random "turn" at controlling the atomoton/vessel that is the Lady of Pain. There is no actual 'entity' that is the Lady. Zeus could be controlling her one minute, then Amaterasu the next, then Asmodeus, then Grumsh, then Seeker, etc. This explains away the Lady's... "unpredictability". No being could force possession, and when controlling the Lady, they were incapable of direct communication with any other being...they could only move around Sigil and interact a bit, with great effort.
Lastly..the lingo!

I know a lot of people love it...but me, exact opposite. Hated it. It sounded...childish I guess. Like it was a bunch of 9 year olds trying to make up words to sound cool, then laughing at anyone who gave them a funny look, then patting themselves on the back for being "so clever". I don't know. Probably just me, but man...REALLY got under my skin.
Oh, lastly lastly.. the Blood War.

I'm
NOT even going to start!!
^_^
Paul L. Ming