Though I agree that Dawnguard on the Xbox has become an open beta, it's not because of a lack of features. I personally really enjoy the quests, new items, new areas etc. The reason I think it's an open beta is because none of the issues the supposed "beta testers" pointed out were actually fixed. The whole beta thing was too close to the actual release date anyway and it was just a PR thing from Microsoft.
Though many players don't have significant issues, a lot of players do. From glitches with Serana, to gameplay crashes, to issues with items spawning, etc. Bethesda's support page for the DLC is already crowded with significant issues, and the best advice they have is either "reload to an earlier save" or "avoid doing that". And this doesn't even include the vampire attacks on towns that people complain about.
Personally, I haven't had many issues on my first character (aside from vampire attacks which have become incredibly tedious to deal with), but on my second character the main quest has become unplayable. My game crashes whenever I try to load a an area and nothing I've done works (restarting the xbox, reloading from an earlier save and trying again, deleting and reinstalling both the game and the DLC, clearing the cache).
P.S. Apparently, if you become a vampire to enter the soul cairn and the subsequently cure yourself, you will no longer be able to enter the soul cairn (I can confirm this on my first char as well). Bethesda support's response to this is "Well you shouldn't do that". I understand they don't usually patch DLC, but if they don't fix these issues I'll be pissed.
I agree with you. The DLC I thought was awesome, all these glitches blow (especially the game breaking ones) and just ruin the game. I think Bethesda is neglecting something very obvious too. Anyone who plays their games comes across procedural glitches that occur when you do something either out of sequence or very odd. If you know Elder Scrolls, then you've got a save you can fall back on and work through it to prevent the glitch from happening. That stuff is forgivable. What is currently plaguing Dawnguard are NON-procedural glitches that are being caused by what I don't know, but are introducing things into the game that are just svcking the fun out of it. So if they think to gloss over the problems they have introduced with this DLC, I will be severely disappointed in them.
Also, I had the same problem with the Soul Cairn that you did. Was a wolf, became a vamp, cured myself to become a wolf again and then was slightly... annoyed, to find out I couldn't re-enter the Soul Cairn. Just so you know, you can become a vampire again and you can then re-enter the Soul Cairn no problem. Two warnings however. First, if you had already previously regained your lycanthropy and you want to be a werewolf, DO NOT re-enter the Soul Cairn as a vampire. Once you've regained your lycanthropy once, you apparently can't get it back a second time.
Also, in the process of switching from a vampire to cured to werewolf to vampire and then cured again, I inadvertently introduced a glitch into my game. Basically, this glitch will randomly turn me into a vampire, so I urge you to be cautious in doing any switching, because apparently there are bugs in doing so.The vampire glitch is extremely annoying (because I obviously don't want to be one) and oddly enough it transforms me into a regular vampire and not a vampire lord. Falion won't recognize this form either, so to be cured of it you have to have Serana transform you into a VL. This doesn't help matters truly, because the glitch occurs over and over and over, so you are better of just being a VL... sigh.