I had done a bit of drinking in Vegas before I first picked up Marvel vs Capcom 3. For the first few seconds of my first match, I had extreme trouble defending properly and landing any hits on my opponent. Within a short time, however, I completely got the hang of it. In fact, I'll take this opportunity to brag that I went on a seven- or eight-game win streak. I eventually lost to a little kid who was no more than ten years old, because I picked some characters that I'd never used before and took it easy on him... or at least that's what I tell myself.
Anyway, you can find all sorts of details about the game system on Shoryuken. I really liked the way that combos strung together fairly easily. The combo system is similar to Tastunoko vs Capcom, but I couldn't really get combos like A, c.A, B, c.B, C, c.C to work. I'm pretty sure I was just timing my inputs improperly. Launchers were a little finicky as well. Some characters seemed to consistently land launchers only after a sweep, while other characters could not do so. With more practice, I'm sure it will become clear as to what combos work consistently.
As for characters, my favorites were Felicia, Morrigan, and Hulk. Once I got over my constant urge to do Felicia's MvC2 "Sand Kick" super (which she doesn't have in this game), I started to do really well with her. She can chain into a sweep, then combo that into a multi-hit rushing super. Her launcher works really well after a sweep, as well. She has a super that summons a fellow catwoman who attacks randomly, like Yatterman-2's robot in TvC.
I found Morrigan's arcing dashes really useful and tricky, much like in TvC. Her jumping Exchange is her aerial multi-hit drill attack. She had a Level 3 Super that did a ton of damage and could even be comboed into in mid air.
Hulk had some nasty tricks. He could air combo into a final hit that would bounce the opponent off the ground. Hulk could then land and OTG with a Super. His standing C had super armor and canceled into his launcher, which could then be canceled into his falling rocks Super. Though he wasn't very mobile, he did some serious damage.
Overall, I really enjoyed the game and found the characters to all feel unique and fun. I had a bit of difficulty mounting an offense with the many characters that had no air dashes, but as Hulk showed, mobility was not totally necessary to be dangerous on offense. I'm actually hoping to see another slow/strong character and a true grappler in the game. There were some brutal grab-Super resets in TvC that might also work well here. Obviously, I'm really looking forward to this game, and I'm keeping my fingers crossed for GGPO online code.