In KOF98, she is relatively easy to play and she is also one of the few characters that don't have as hard of time defeating the top tiers (i.e. Iori, Daimon, etc). And, no. Nothing about Mai Shiranui's play style in KOF is even remotely similar to Kasumi. Mai has quite a few good pokes (st.A, st.B for example). Her air control is also very good. The player can take advantage of things such as neutral jump B because he has quite a bit of range on it and stays active for a bit before she lands. Combo starters include cr.C, or cr.B into close st.A (because close st.A will cancel into her special moves). It is important to note that she has to versions of herself in KOF98 (along with a few other characters). The regular Mai has some elaborate juggle combo from one of her DM's. The EX version has access to better ground based combo because of a special move that allows her to free cancel into her Ryuuenbu (qcb+B, a move where she creates a bigger version of her fan to swing at the opponent. It can also function as a good anti-air). I tend to favor Mai's EX version because of combo damage and pre-emptive anti-air qcb+B. In 98UM she also has Kagero no Mai which has invincibility on start up but is very unsafe on block (the B version is a bit awkward to punish at first, however). In KOF02UM, she is a tad better than she was in 98 and her ground combo damage is better, especially if you start from st.C (specifically st.C, df+B, qcb+B, free cancel into Ryuuenbu). Her air control is also a bit more... crazier to put it lightly. However, according to Dream Cancel, Mai is still somewhere in the mid tiers but much like in 98, she is manageable.
(I don't know anything about her incarnation in OG 02).
In KOFXIII... well start here (It's a long story):
