Yah, horseboys. It would be nice if they looked a bit younger (they're called horseboys for a reason, they'd be teenagers really) and they should really have darts (smaller but more carried) rather than large javelins (shortbows would also be possible if not quite so common, that would be more interesting IMO) but anyway. Other then that they're accurate AFAIK.

Hopefully the Irish will get another late period mounted skirmisher unit...which will help immensely.
The TotalWar devblog mentions that they eventually get Mounted Calivermen, which should be very effective against heavy units if used correctly. Historically skirmish cavalry were a big part of Irish warfare (the only part which was adopted more widely; Hobilars are inspired by English experiences in Ireland) but I hope they get a few decent melee units at least. A heavier greatsword or halberd armed Galloglaich unit for the later era would be cool.

I thought the Mayan unit was straight from fantasy-land as well, but I don't have the knowledge of the area to really now if they aren't in a historical account, and it does seem like a good idea against heavily armoured enemies (it's cool to see when a force which is wholly superior on paper gets beaten because their enemy think outside the box or do something "not fair")

Antagonist

I thought the Mayan unit sounded fantastical