Urban Arcana isn't really THAT bad. It just isn't very serious.
From the art, they were obviously going for a sort of D&D Punk thing, what with the body-mod dwarves and sk8ter drow.
Unfortunately, stuff like The Prancing Pony fast-food joint, magical cell phones, leather jackets of biker-studliness, and Kobold Kommando gave the whole thing the air of a big joke. And, really, I think they couldn't HELP but make D&D Is Coming Through The Rift! into a big joke. D&D is way over the top, right into the range of Fantasy Super Heroes. I can't think of any popular fiction that really puts fireballing mages against dragons in down-town NYC. Especially not kitted out with outrageous gear like magical cell phones and magical lick'n'stick tattoos.
I guess, to me, it had sort of a juvenile charm that might have attracted the 13-17 crowd. Y'know: "I wanna play a bugbear with an eyebrow ring who dual-wields katanas!" kind of stuff. The short run of it I played, the GM was new but good. He allowed it to be both tongue-in-cheek and rather serious, which is really the only way I could see a group of people 25+ playing that setting.
As to what the sales were like for Urban Arcana ... I haven't researched it. I know I bought it, just because it was the first setting book for d20Modern and it had Incantations in it. My secret hope at the time was that if enough people picked it up, they'd do full-size hardcovers of some of the setting ideas that DIDN'T suck ... so apparently it didn't sell well enough for that.
--fje