I'm disappointed but open to being moved towards "excited."
I wanted either a new setting designed for 5e assumptions or pretty much any classic DnD setting instead of an out-of-left-field move like this. The thing for me is that MtG has a completely different, and unique, magic system that's not directly compatible with DnD. It has different races, assumptions, planeswalkers, etc, that become a mish-mash if you start cramming them together with all the rest of the existing dungeons and dragons world.
It reminds me of when I saw Hasbro come out with Star Wars Transformer figures that literally looked like Boba Fett, Darth Vader, et al, turning into spaceships. Its cool to have a Star Wars line with new stuff and it's cool to have a new generation of Transformers, but when you mash them together, something's got to give. Something about this setting is going to be Procrustean. You're going to have to chop some DnD off at the knees and some MtG off at the elbows to make them fit in this new box together, and that proposition is more disappointing to me that what they could have done if they had just made something grow directly out of the 5e core. Han Solo loses some of his aesthetic if his body is also expected to turn into the Millennium Falcon.
On the positive side, I'd love of a setting filled to the brim with magitech. I'd prefer Eberron, but if we can get a magic gun-wielding artificer, magitech items, and a host of magitech subclasses, I'll at least be hyped to loot all of the toys the setting includes.