Riders and Ultramen are pretty straightforward as normal characters transforming into their heroic forms via the Alternate Form power, where they have boosted abilities and other goodies. Multiforms and some powers like Decade's will be troublesome, but those are a case-by-case basis.
Sentais gets trickier, since they have a lot of team and theme-based abilities where the game system is mostly focused on the individual. For example, their combined weapons system will likely require a Flaw of all members being present. The trickiest thing to get done in M&M will probably be the mechas, which I don't think I'd want to get into the details of as it can be very subjective to how it can be done.
Generally, that's how it goes as M&M is a generic superheroes system. You should try to get started by playing around with the system and create an a test character to get a feel for how comfortable the rules feel. For people interested in playing in a sentai heroes-only game, they should probably try their hands at one of the better editions of BESM, which has more genre-appropriate conventions built into the rules.