Just finished the demo about an hour ago. First impressions are pretty good, though I should temper that by saying it's a very limited demo. All of the character customisation options are locked out, as is the inventory system.
Still, though it takes a minute or two to adjust, the new combat system is a considerable improvement over DAO's and reminds me of the difference between ME1 & 2 in how everything was streamlined and improved. It's still basically the same system though, just that the abilities are far more useful, the animation is a lot snappier and the action feels a lot more intense and immediate. There's still that odd RPG-ish thing where you can have 3 enemies standing around you waving swords around without much of a feeling that you're actually making contact, but you can't have everything.
I love the ME style dialogue wheel and the inclusion of a voiced protagonist. The silent warden in DAO always bothered me a little so having the ME style interactive cutscenes was a huge improvement for me. I've noticed some complaints about not being able to select specific dialogue but honestly, seeing what Shepard (and now Hawke) comes out with after you pick a general tone and direction is half the fun. Even better now there's a little icon that tells you if what you're highlighting is going to be aggressive, joking, peaceful minded or hardened (I think that's what the diamond means!) I don't know about anyone else but I got a nasty shock a few times in ME2 when what I thought was a friendly chat between my FemShep and Jacob suddenly became much more flirty than I'd expected, so I hope this is a feature that finds it's way into ME3 in some form!
One thing that did feel odd is that they've shifted the overall style of the game a little away from the "realistic" (if a little stiff) feel of DAO into something a little more stylised. The darkspawn look quite different and have this odd almost exaggerated ape-like gait that I'm not too crazy about. I don't think it's a spoiler to mention that a certain witch of the wilds puts in an appearance early on and speaking of her appearance, she looks almost nothing like she did in DAO...which is a little odd considering the opening of the game takes place right after Lothering fell to the blight. Mind you, she is a shapeshifter so it matters not. More to the point she looks much better and more in line with her reputation in this new guise.
Bottom line, it looks very good and I'm glad I pre-ordered it already.
[EDIT] Oh, and this is the first Bioware game where I might actually stick with the default female appearance!