Why ulduar is one of my most fondly remembered raid.
1. Variable difficulty. Everything had a variable difficulty setting bar 3 bosses.
2. Graphically one of the most superior raids ever released. That extends to gear,bosses and the zone itself.
3. Pick your own progression path. Choosing kill orders and being able to skip bosses allowed more time to focus on specific goals every week. IMO far superior to extended lockouts.
4. Intresting hardmode triggers, not some boring toggle to "insert mode here"
5. Plenty of content (relates to point one)aside from the clearing and meta achieve there was a whole bunch of quirky achieves to keep a raid team going for awhile.
Just to sum up, I didn't actually get to do alot of ulduar while it was current content due to PC issues and I still rate the place on par with Kara,SSC and TK.