If game is good, me want more game. Pretty simple caveman logic there.
As for good and bad, regrets and such... anything small is typically not worth the trouble, like all those Oblivion houses and Mass Effect guns. It's the bigger stuff I like, the Fallout expansions and Mass Effect 2 missions.
My one big annoyance with it is that this content is time-limited by its very nature, once the servers go down and you change hardware that stuff is gone. That's a bummer, and I always try to remember that what is on the disc is the true game that will last forever.
Oh? Is that true for all games? I thought if you downloaded it it was yours? I wasn't aware that was time restriction?
Xbox Live for the 360 will go down someday just like it did for the original Xbox. At that point everything you bought only exists on your machine, and cannot be required.
Unless of course they have full backwards compatibility with all downloads from the 360 on the next Xbox, which would be nice, but I'm not betting on it.