I have to agree that the lack of release notes makes the preview of very limited value. It's completely impractical for us to submit bugs about every little thing that we have no idea if it's even intended.

For example, Vitality +20 now appears instead of Toughness. Working as designed? Bug, held over from the Enhancement respec?
No unique loot has been reported yet from the new quests. At this point should we flag that as a bug? Is it not implemented? Do they not have any unique treasure?
The quests don't have an epic version. Intended? Bug? Being delayed until the xpack so they can be lvl 26+ quests on epic?
Iconic character cannot be reincarnated in any way. Bug? Limitation due to the current preview? Intended design?
There appears to be no new Monster Manual. Intended? While I'd love to submit a bug report that there aren't enough MM volumes, I don't think that's particularly useful for anyone involved.

If you want better bug reports from us, give us what we need to make informed decisions.