I played Omerta for a couple of weeks last summer and, uh, was colossally bored. I think it's mainly due to the fact that the core mechanics, the select crime -> click -> wait a minute -> select crime -> click -> wait a minute bit of it.
However, there were some interesting elements to it - permanent death particularly caught my eye. The trading is also decent enough, but the vast fun of the game comes (I am told) from being a part of a family. The communities around these are strong and form the bits of the game that you'll actually remember fondly.
Oh, and I would recommend NexusWar
as my browser-based poison of choice. It's essentially inspired by Urban Dead, but the interface and things to do are massively increased. It's got a greater longevity - my characters have been rattling around for a year or more now and I haven't seen it all. It's also, like Omerta, got factions as its mini-communities amd the limited territory means there is actually something to fight over (this will be futher expanded in the 1.5 update, though it's a way off)
Finally, the game world is some two to three thousand players with some eight to nine thousand characters, so you really can make a difference - everything plays on the same server.
Pimp over ¬_¬