NBS beat me to it.
The start of this video (with the tentacles etc.) reminds me so, so much of BG3, with the mind flayers. I watched some of the trailers to BG3, and when they show mind flayers actually implanting a victim (you) with their larvae ... *shudder* ... I couldn't watch. Too horrible.
Do you ever watch a scene that fills you with incipient dread of something that you know is coming but are powerless to avoid? That's exactly what BG3 did, which is why it was so effective. It made me instantly think "I'd like to experience this", and I've never played BG1 or BG2.
Even without the BG3 graphics (which are awesome), the BG3 story feels like it instantly "draws me in". That's what a good trailer should do. It shows you who you should go after, and you know you'd like to go after them, even if you don't know why, and you don't know how.
But as for the DA4 trailer ... well, it just seems like one of two things:
1. It's a collection of the best "moments" from cutscenes of the game; or
2. It's like the trailer for DA3, but just more of the same. More dragons. Yay.
It doesn't give you any reason to play it. You're going up against gods and dragons, and the Veil is being ripped apart? Um, isn't that exactly what you did in DA3 against Corypheus, except that he was an ancient darkspawn (and was never very compelling as a villain)?
I looked up more of this, and found
this article on Tech Radar. It's all worth reading, but these struck me as significant:
The story will visit new locales including Rivain, Weisshaupt, Arlathan, Minrathous, and the Deep Roads.
From what we've seen so far, Solas is hellbent on opening the Veil, a portal that'll bring demons spilling through it if he succeeds. Varric, Rook, Lace Harding and Neve Gallus are the characters confirmed so far. It's also been revealed that there will be seven party members, with all of them being romanceable...
Fans of Dragon Age: Inquisition will remember Solas the elven mage as a party member who joins your team early on in support of your efforts to prevent the emergence of dangerous magical rifts caused by the evil mage Corypheus. However, it turns out that Solas was the elven Dread Wolf the whole time and was playing the long game, looking for a way to break the veil between magic and reality on his own terms, not Corypheus's.
So:
1. Yes, most of these locations are new ... but we've see Weisshaupt in DA3, and we've see the Deep Roads how many times now?
2. Solas wants to open the Veil. Isn't that what Corypheus wanted to do in DA3? And I thought we sealed the Veil?
...and...
3. So, the whole point of DA3 was that Solas wanted to thumb his nose at Corypheus. "You think you're the villain? Hold my beer and watch this."
I'm sure that, in typical Dragon Age fashion, once you stop Solas (which won't be easy), we'll find out that something else out there is really behind Solas (or trying to use him, or something). But to be honest, after having done all that hard work in DA3, I really don't care anymore. It feels like being cheated.
You know the sort of thing: I did all that work just to start all over again? The heck with this, I'm going to play Clue with BBP instead.
Sure, he was crude, but he was funnier, and and a lot less melodramatic. 
I'm going to play Baldur's Gate 3 instead, once it's on sale. 
I've never played a Dragon's Age game, but I always keep the save games for big RPGs (Mass Effect, Elder Scrolls). So, Yeah, I would still have them. And don't most of these games backup saves to the cloud. Steam does, anyway.