I, too, was a little underwhelmed. I don't think the ending was terrible, it just wasn't very impactful. Going by the trailer, with the WoL wandering an empty wasteland alone and bereft of succor, I was expecting (or, hoping for) Really Bad Things at the end of this patch, for example:
the WoL did not get to Hien and company in time, and they were killed by AsciZenos, who was finally destroyed for good when the WoL went Super Saiyan in a fit of rage and despair (yeah, very cliche, but it would be satisfying). Now the WoL has to go through Shadowbringers carrying that weight; the guilt of, for the first time, being too late.
This goes right back to what I said ages ago about the ending to HW, when Thordan looks at us and sees a profound darkness. Fordola even sees it, when her articifial Echo gives her a glimpse into all the terrible things we have seen and done, and she asks how we can stand there, unbroken. It is a side of the WoL that I have been wanting to explore for a long time, and maybe ShB will do that, but I thought the end of SB would have a been a perfect time to bring that back. We need something to turn us into the Warrior of Darkness other than the usual "it's the right thing to do and someone has to do it" reasoning that defines most of our actions. I still want to see my character as a man with doubts and fears, as someone who on occasion needs the comfort of a friend, instead of always being that comfort.
I'm still psyched about Shadowbringers. After all, none of us knows how the story will play out.