Impressions - This felt pretty much the same as the TGS build. Not a lot had changed, other than X-Factor's scaling being in place, and having a lot more selectable characters.
MODOK - Awkward. Up doesn't jump, it flies, and it can be really difficult when you accidentally go into this fly mode and just want to land. It takes a lot of time to learn to move around with him and figure out where his normals go, and figuring out where all his projectiles go will be key to making him a terror. Even doing a basic air combo with him takes a little finesse. All in all, he seems powerful, but has quite a learning curve.
Arthur - Awkward. Contrary to the Portugal reports, Arthur can double jump in this build. The lack of a ground dash makes moving with him very difficult, and learning which projectile goes where is very important. You cannot refresh his golden armor. You have to wait for it to end, summon new armor (silver), and then upgrade to gold again. He is pretty darn hard to win with right now.
Magneto - Very fast, easy to combo with from any range. Great projectile, Force Field assist was interesting, but he was hit out of its startup a few times and I stopped using it. Air combos are easy, but he doesnt get much damage in the corner from OTG shockwave. Very versatile character.
Storm - She is SO good! Slower than in MvC2, and a little less range maybe, but loaded with options and damage. Air lightning super doesn't cause a free-fall, so DHCs are hard. Hail Storm hitting OTG is crazy, and it does so much chip damage. She will be very popular.
Spider-Man - I stopped playing him quickly because of his floaty jump. Jumping feels like Dhalsim almost, and I wasnt getting used to web zip very quickly. Wish I'd played him more, but he wasn't clicking for me right away and time was short.
Tron - Played her once. She seemed good, but drills traded with stuff a lot. Getting just one hit from her drill vs even a weak attack is not a good trade.