Okay, don´t listen to the bombcast guys here. They might tell you that playing it on the Vita is "okay" and whatever. Here´s the deal: It´s only okay if you can deal with a really noticeable amount of lag.
There are people who play on TVs with all the picture enhancements turned on.. the amount of lag that adds is severe- playing PS4 games streamed to a Vita is maybe not as severe- but still pretty bad. I wouldn´t recommend playing anything other than a puzzle game on this if you don´t like your controls to feel all mushy and weird.
AC4 might be tolerable (exploration and ship combat) and the on foot combat is so easy it doesn´t really matter... but it will still feel like you´re wading through a swamp all the time. And don´t even try to play a shooter. It will drive you insane. Oh and it only runs at like 30 frames per second on the vita screen.
Edit: It looks just fine on the vita (not as good as a big TV of course). But looks aren´t everything.