There's a lot of effort and work that have been put into the visuals
If you have seen their concept arts, you'd know how decent all the models are
I think it would be better if Blizzard has been lastingly teasing us with those arts to be honest
As for the other visual aspects, I think that a) they got the tile textures wrong, b) that some of the character animations feel
too cheap in the cinematics, and c) that the rendering is not that impressive in regards to the modern standards
(but I guess limited render is something that all RTS games have to deal with)
Yes, keep in mind that what you see in the trailers is still a work in progress
All special effects are either absent or unchanged; look at how the rifleman shoots without any fire, or how the blademaster simply spins around himself without any effects or whatsoever in the trailer. The spell effects (Dark Conversion, Devotion Aura) and the missiles (Necromancers', Towers') are all the same as in the original game.
However, in the midsts of the gameplay it looks MUCH better - take a look at
The Culling mission for example