I was a big fan when it started, I stuck with the Spider-Man run pretty much until the end of the Bendis/Bagley partnership, I think I stopped reading just before Miles came into things. (So missed out on that UF #4, doh!)
At the time I loved the original Ultimates run and dipped into X-Men / Fantastic Four for while. Like you I didn't have much exposure to their mainline titles so I really enjoyed the fresh start approach but as I've been recently trying to trim down my collection I reckon I'll offload them soon. There's a lot of good reading there for a kid somewhere to pick up and hopefully enjoy.