I'd recommend Gurumin: A monstrous adventure (also made by Falcom who do the Ys series), Half Minute Hero, ZHP, Riviera, Yggdra union, and Knights in the Nightmare.
BTW, if you buy Knights in the Nightmare now it comes with a download code for a free copy of Yggdra Union. I got that and all I've been playing is Yddgra Union...haven't even gotten around to Knights yet. From what I understand the entire first print run is supposed to have the code but if they print more later it will not include it. It came out pretty recently so you should still be good for now.
Also, Ys Seven is great. Can't recommend it enough.
I honestly didn't like the PSP Lunar very much. Looks pretty, but it's very
slow paced. Long (and frequent) load times, painfully slow unskippable attack animations, etc. It's a pretty easy and simplistic game too, so I found myself having to multitask when I played it or else I would just get bored. In battle I would literally cue my commands, put the PSP down, and do something else while I waited for it to be my turn again.