I've been running my Friday night Stonehell game for nearly 30 sessions now, and it's been a fun experience. It's absolutely scratched my old school dungeon exploration itch, and watching my players get familiar with the dungeon, and use that knowledge from game to game is really gratifying. Of course it hasn't all been perfect. As with any long running campaign, I haven't always brought my A game, either from illness or just not always being in the mood.
My game group has shifted, as some players who preferred the more role playing elements dropped out, and new players filled the vacant seats. It's been a great way to meet new people though! One particularly interesting aspect is the gender balance. Early on, it was predominantly a female group, with many sessions only having women playing. Currently it's a more evenly balanced group, but still tends toward female majority depending on who attends.
From a top down view, my players have explored most of 1A (Hell's Antechamber) and 1B (The Quiet Halls), and have explored good chunks of 1C (The Contested Corridors), 1D (Kobold Korners)and 2A (The Asylum) and 4B (The Living Caves East). They've also visited the Reptile House, Without Doors, Hobgoblin Redoubt, The Monster Dorm, and so very very briefly The Chamber of Many Faces.
One thing I've noticed is that while the whole dungeon is open to them, they seem to really like having a few plot hooks to bite onto. Ages and ages ago, I mentioned Malfesance Nul, the guy who talks to the dead hiding out in the Quiet Halls, and in spite of the most experienced player's objections (also the most experienced character's objections) that seems to be the quest du jour.
Seeing how the NPCs in Stonehell react to the PCs has been a blast. Since their initial encounter with the berzerkers they've been on really friendly terms. It hasn't hurt that every time the party has encountered them that they've shared their beer. On the flip side, the cowardly actions of the death priests looking for Malfesance Nul in the face of the ghoul assault means that Bob and Co. are likely in for some pain if they happen to encounter the party again.
Rocky, and his love of quartz resulted in the party stumbling on 2 of the most powerful creatures in the Dungeon, and living to tell the tale, not that the party has any idea who those people were. I'm also not sure if they've groked that Rocky doesn't always tell the truth... Even when cryptic, they seem to think he's telling the gods' honest truth.
Design wise, I still (mostly) like Stonehell's layout. Maybe it's because my players (and therefor I) have spent so much time in 1A that it's the quadrant I'm least happy with. Then again, at this point it's pretty depopulated, so they tend to just breeze through it. The Contested Corridors is pretty empty since they all but wiped out the orcs. The northern half anyway...