1. Raiding is intense and buffed. You can count roughly 270% buffed.
2. All dungeons are working fine enough.
3. Vanilla questing is fine enough and close to perfect escept some chat scripts missing, but TBC a lot of quests are bugged in Shadowmoon Valley, Netherstorm.
4. Northrend, a lot of quests got bugged and yet awaiting to be fixed since 3-4 months. I went northrend on 68 on my hunter and i had to almost do each and every quest in northrend to get to 80. However i skipped dungeon quests a lot because RDF is disabled and its boring to spam global for 30 mins to 1 hour to gather a group for an NM dungeon.
5. about DB, if you asking about player DB, nope. if you asking about spells etc then yes. if you are asking about raid content, nope not at all. read first point.
well, for ur 4th point, i can say i didn't face many bugs on quests but i haven't finish the quests on icecrown and stormpeaks yet. i just remember only 1 bugged quest. dont even remember i had more or not...