I find the city kinda boring. All the buildings are completely empty, which I think takes away some of the fun of exploring an empty city. I like the sewer system quite a bit, some of the mob spawners are very deadly while others are a complete joke, but the random rooms are nice. I like how some of them have brick doors and others iron bars, so sometimes you can see what you're about to open and sometimes you can't.
I've so far found: enderman, spider, poison spider, silverfish, creeper and pig zombie spawners. Enderman and pig zombie are useless, because I don't attack them
. Poison spider and silverfish are insanely dangerous, because those mobs fit through a 1 block hole (I had a close call with both, only got hit once by the poison spider but the poison took me down to 1 heart, and there were about 15 silverfish spawned by the time I opened that room).
As far as treasure goes, I've been fairly lucky I think. 2 diamond swords, 2 diamond picks, 2 diamond chestplates, 2 diamond hoes, a buttload of gold and iron stuff (swords, axes, armor, etc), 4 or 5 powered minecarts (idk what I'm going to ever do with them?), a map, a saddle, 3 buckets of lava, and various other things. Only found 2 redstone so far, but that made me a radio tower. It's boosted to the max 550m, anyone who gets the message is free to use my place to live, just don't get all stealy on the chests (there's lots of free food!).
Also, made a nether portal and a fishing pool. I can't seem to make fishing rods myself, but found one in a chest, so I can get raw fish for now. I haven't been through the nether portal yet, and probably won't take the chance of dying on the other side, for now at least.
Overall, this has been the easiest solitude experience so far. It's interesting how the city changes what's rare (coal, anyone?), but I'm still a little disappointed with the empty buildings. They could at least have some rooms.