Maybe the next thread of this series could be focused on future DLC only, rather than on dawnguard and future DLCs, given the understandably increasing number of threads on various key points of Dawnguard?
Anyways, here is my opinion on what I heard of Dawnguard.
What I didn't like : That the vampires don't look like the Volkhiars of the lore, who pass through the ice of frozen lakes. Well, I suppose that "Immortal blood" was romanced, and then, not entirely reliable, but this makes me sad, cause the Valenwood vampires it describes seemed freakingly nice to me, and now their existence and nature is questionable as well...

The name "Fort Dawnguard". I find it a little dumb, they could have given it a "real" name.
The association between vampires and bats had never been done in past games.
From the trailer, it doesn't seem that we'll discover more about Lamae Beolfag and the Shrieking Winds. But could Lamae Beolfag be the root of porphyric hemophilia and not sanguinare vampiris?
What I am not sure to like or dislike :The story. It seems epic and I am looking forward to play it, yet one of the options seems to be very hard to assume in future DLCs and games. Yet this is a matter of personnal opinion, my personal taste and appreciation of it doesn't prevent me to see the immense work that has obviously been put in this DLC and to consider it of great quality. Thanks Bethesda !
What I like (very very much) :Crossbows ! Finally

New Dragons! We need tougher Dragons, who are a real challenge even at higher levels.
Death hounds ! I wanted to see the Daedric Hell Hounds, and it seems that I'll get to see some of their relatives

Armored Trolls ! I have always suspected that some Trolls were intelligent enough to craft things or at least use tools or weapons. This opinion was substantiated when I discovered that the game Dawnstar featued a hierarchy in trolls, and even trollish weapons (I think there was a Troll warhammer)
Frost Giant! Epic !
Soul Cairn ! I am impatient to visit it.
Dragonbone weapons ! I love them already.
The gargoyles that come back : the more diversity among creatures, the better.
New perk trees.
New lore. It seems that we'll have new lore about vampires, about the Soul Cairn, and possibly also signs of an hypothetic, embryonic culture in some tribes of trolls.

The likes outweigh clearly the dislikes.
What I hope : That there'll be updates for Dawnguards to meke it better, as it is the case with Skyrim.
That we'll get real bats. I find it
so frustrating not to be able to interact with the swarms of bats appearing in some dungeons. Come on, you know you want to make potions with bat wings or eyes !
That we'll get tha Axe called "Wings of the Queen of Bats" that was http://uesp.net/wiki/Morrowind:Wings_of_the_Queen_of_Bats in Morrowind, with pieces of lore around it.
That there'll be Troll weapons alongside their armors.
The spectral mount! We all want a Daedric stride !
That we'll get a soulbug companion as seen in the game jam, and whose texture looks similar to that of the spectral horse of the trailer.
That we'll be some day able to cast spells without being forced to dismount. This, alongside new spells affecting the mount (giving it a frost aura, or making it faster, for example).
That we'll get some time a "Dragon shout" perk tree.
That there'll be a vampiric perk allowing us to breathe underwater and pass through the ice of frozen lakes without breaking it, to grab opponents from beneath (as described in "Immortal blood). Also, some underwater combat vampiric perks would be nice !
That I am wrong, and that we'll discover more about Lamae the Blood-Matron and the Shrieking Winds she spawned.
And you, what are your thoughts?