I had stopped playing UO since 2001 or so and I am considering to return as I like this game VERY much. I opened a free 14 days account and ran to Monglow, Minor, and even Britian and I see no people. What's up now? Is it too silent right now?
A lot of the old facet's cities are bare these days. A strong reason for that is that most players (and this is only in my experience, not speaking for everyone of course) are in the Stygian Abyss and the newer facets, especially Luna in the Malas facet. That is the current "West Brit Bank" if you understand the reference.
Luna is a hotspot because all of the amenities of a town are very close. Your bank, stable, provisioner, etc. are all within a 2 screen radius. On top of that, you can find almost anything in the vendor houses around Luna's core.
As far as the old dungeons go, they do not provide loot that is on par with the stuff you can get in the new Stygian Abyss dungeon. If you want to support your characters with modern gear, weapons, and artifacts, Stygian Abyss is the place to be. So most hunters are there.
A lot of the Felucca population takes part in faction PvP and Felucca-based champ spawns, none of which takes place in towns (unless some faction fighting is going on in a town). Felucca-based dungeons can be dangerous though as the champ spawn guilds can be ruthless from time to time and champ spawns are in those dungeons.
Some good places to try are Luna and even New Haven. New Haven has a lot of newer players (and returning ones), as well as people who help them.