While in the vampire playthrough, you dont get a single main quest to attack the dawnguard?
And that the vampire armor, hood, form, and everything are accessible from a dawnguard playthrough? Yet the dawnguard gets specific spells and such that vampires dont.
The vampires have a drain life spell that is unique to them. It's not all that great, but its unique

. You can also get those Dawnguard spells as a Vampire. You have to be crafty to get them, but it's possible.
This one was just a general disappointment. After killing Harkon, everything continues as normal. After his death it was anticlimactic. You're technically the lord of the castle, but no one even refers to you as lord. The only thing that changed in any way was Harkon is gone. I didn't really feel like the hero, the savior at the end of the game. Nor did I feel like the ruler of the castle.
People had that complaint about killing Alduin too, it just seemed like nothing happened. It reminds me of when I played one of the fable games and used a wish to bring everyone back to life. I never meet any of those people, and all I got was a statue. I just sat there thinking, thats it? And got mad I didn't bring my dog back to life lol.
If I recall correctly the dialog around that event revolved on Serana taking over. Once Harkon was downed I do believe that Serana became Lord of the castle but was having so much fun adventuring with you that she decided to keep the party rolling....so long as you were still into it.
What I gathered about Alduin was that not many people knew exactly what you were doing, and those few that knew didn't really understand. So the enormous concept of traveling to Sovngarde and defeating The World Eater is completely lost on most; which explains the lack of
Pomp and Circumstance.But that's just my point of view
