I've been playing NetHack since December 2013, so just about 10 years now. I've played on Friday the 13ths and on new moons, but never had the opportunity before to play on this double stroke of bad luck, as explained here. I still play the game pretty regularly--as in like, all the time--so I have a pretty good sense of what "normal" luck feels like vs. today. Here's what I observed based on a few runs:
-Enemy spawns, both the number and the quality, are cranked way up. This is actually a somewhat good thing for my usual playstyle--I almost always play pacifist tourists up until Minetown, so that I can get the most divine protection out of whatever gold I can scrape together. If you don't know what any of that means, don't worry about it. The important part is that if you're not killing things yourself, you're relying on your pet to kill things for you. Your pet, like you, gets stronger the more things it kills, so an abnormal number of spawns on the early level lets you feed it a lot of kills so that it's better able to protect you. This wasn't too dangerous in the early going, though I did have to watch out for a few foxes, but once I got a character off the ground I felt like I was fighting the extremely dangerous mumakil more often than usual.
-With one exception, traps didn't seem more vicious than normal. I didn't die at all to the usual poison spike traps, falling rock traps, or rolling boulder traps. I did come pretty close to dying due to a polymorph trap serving up a way out-of-depth master lich, but fortunately I kept my wits about me and was able to burn an E-square onto the upstairs before it completely destroyed me.
-It didn't feel like I had a harder time inscribing Elbereth, which is always a bit of a crapshoot, than normal. But I definitely did die to a failed attempt once.
-Starting abilities and stats did seem a little worse than usual. Normally, one of the only things a tourist has going for it is a healthy supply of food to start out with, but I still managed to starve to death within spitting distance of a grocery store in Minetown, thanks to a stingy roll on my starting inventory.
-Related to the above, it seemed like my deity absolutely hated me. Under normal circumstances, once a certain number of turns has passed, it's safe to pray to your deity to help you out of a jam. If you're extremely low on HP, they might fully heal you; if you're starving to death, they might fill your belly; that kind of thing. Well, not today. The only result I had from prayer, whether I was trying to get out of a life-threatening situation or simply trying to make some holy water at an altar, was "You feel that the Lady is displeased."
-As noted elsewhere, against all odds I had some of the luckiest finds of my Nethack career today. My very first run yielded what turned out to be a rare Amulet of Life Saving, and I wasn't the only one. And my final run, the one I'm actually still playing because it went so well that I didn't die, served up Grayswandir, the best weapon in the game. This is something that is almost always either my first or second wish, and here I found it naturally generated on an ordinary floor, for the first time ever. Weird!