Ninja Theory must have thought the old title really wasn't cutting it, and I can't really blame them for it. Hellblade does sound like a Ninja Theory game, but it didn't reflect the new direction they were going for with this one.
Hellblade: Senua's Sacrifice [official site] should more accurately reflect the two souls of their work-in-progress, pairing their typical hack-and-slash action with an uncommon attention spent on accurate portrayal and characterization of mental health issues. The new trailers lets us listen in on Senua's inner monologue.
It's old news that the team was collaborating with a psychiatrist and professor of the University of Cambridge to realize an honest and realistic representation of Senua's struggle with depression and even psychosis, without recurring to the usual stereotypes. It's too early to say if it's paid off, but the trailer seems to be a promising start.
I'm enjoying how much they're focusing on story, characters and atmosphere in their promotional material, even though they have barely shown what the actual game plays like. It's Ninja Theory so I wouldn't worry too much about the action being poorly realized, but if you are consumed with preoccupation, this is a collection of bits of gameplay. There is fighting, but there is also exploration, and the storytelling is not relegated to cutscenes. Keep in mind that it's from many many months ago, and things may have changed since then.
Hellblade is being developed as an "independent AAA" game, with a small team of 15 that can still make use of the resources of the Ninja Theory studio. They're also being very open with development, regularly publishing new dev diaries. The latest one goes over how to create believable animations and responsive controls with just 2 animators.
Release is scheduled for 2016, but no word on exactly when.