I found out yesterday that you can see scores on the server, including a record of every game you have ever played. My win rate is 0.63%
One guy has a run of 138 consecutive victories. I have no idea how.
I don't have many tips, that was by far my best run. All I would say is that both times I've completed it online my character had a great shield value with reflection. Resistances also seem to play a huge part. Once you get those up then nothing can really hurt you apart from torment, damnation and smiting. The game becomes avoiding monsters who can cast that, or killing them as quickly as possible. If you've got a decent shield then physical damage becomes less important, unless you've been tormented down to low hp and then the odd hit might kill you. My AC for that character wasn't anything brilliant.
The Hells and Pandemonium were pretty similar difficulty. Both full of fiends and tormentors and hellions, no other monsters matter. The Hells have that shitty thing where they attack you every 20 turns so you can never really rest. Trick is to just run down through as quick as you can and don't be afraid to escape again to the top if you have problems. You're always making it easier the more monsters you kill. Scrolls of magic mapping are really useful for that.
Tomb is the worst. Greater Mummies and Mummy Priests are as bad as fiends. I bottled that.
Qazlal is cool. Repel Missiles, extra shield, damaging clouds all around you and Disaster Area is fucking brilliant at high invocations. Fields of lava. The only downside is that you are basically at top noise for the whole game, so you get a massive rush of monsters whenever you enter a level.
I almost died a couple of times, like down to 3 hp with a Pandemonium Lord in view. In those situations Scrolls of Fog are absolutely your best friend.
Probably one of the best gaming things I've done in ages. Proper nervous at times. I got lucky in that I got a decent Holy weapon, which really helps late on.
If you get down to half HP then it's time to start escaping, or at least thinking about it.