So I got to play a couple more of hours of straight Mai and I'm starting to get a feel for her, here are my thoughts and some of may have been mentioned before.
I struggled with her initially because I didn't really "get" her. She lost both her command attacks, her MaxCancel combo is by far the lowest shown in the technical references (due to damage scaling from her DM) and she even lost her anti-air. I was about to chalk her off as fan-service.
Then I noticed her pokes; all of her ground pokes near and far are good. Far C is fast and kinda acts as a pseudo anti air. Far D is meaty, has good range, and has a nice upward slant. Far B has good range and speed. Far A is fast and cancelable. Next, I realized about her priority. Sick. I'll be the first to admit, her priority is pretty disgusting and I think it was designed that way to compensate for what she lacks (I beat Kyo's wake up DP both with her j.B and j.C on different occasions). She has excellent air normals, in particular her j.CD is real fast and her crossups are good (j.C, j.B, and I think even j.D). Her air throw is extremely threatening when you factor in her sheer speed. Everything combined makes her have good offensive pressure and helps make her the perfect battery character.
Now the bad. Once again, I've only a couple hours under my belt with her but it feels like if you can't get your opponent in the corner you can't really do any real damage. Mai's d.B, d.A/s.A, hcf+D combo is hard to hit confirm as well and we all know what happens if they block your hcf+K. Her air.qcb+P is not safe either. Her only mid screen combo that's decent is her jump attack of choice, d.B, d.A/s.A, Ex Ryuenbu, hcf+D (which is cool because you don't need a cancel). If you do d.C --> C Ryuenbu (qcb+C) spaced even slightly apart, it'll not combo making you look like a super n00b. Speaking of spacing, her jump arcs needs time getting used to because of her speed, making you miss the opponent when you go for jump-ins if you haven't quite adapted yet. Other than that you just poke away or j.CD them and overall just zone them until they are in the corner. Even when you get them in the corner, her Ex Ryuenbu > C Ryuenbu > C Ryuenbu > air throw is so picky on timing that it's best off skipping the last C Ryuenbu and going for the air throw. Much like Hwa Jai, she doesn't have much mid screen option but turns in to a monster in the corner (especially in HD).
I want to make special mention that her Ex Kachosen (qcf+P) is extremely fast and catches people off guard. Even her C Kachosen is fast again (or at least in my memory her old ones were kinda slow), and somewhat abusable despite not having the traditional fireball-uppercut shenanigans.
In hindsight, I think SNK did a good job taking an cookie-cutter character (jump attack > stand attack > command attack > special attack) and made her gameplay more interesting. All in all, despite her lows, her highs compensates and I would play her in the mid tier section.