PoPoLoCrois is a straight-forward RPG and generally well done, but at times slow and repetitive with uneven difficulty.
The storyline, while not exciting, is solid. You play the part of a young prince who is trying to awaken his mother, who has been in a deep magical sleep for 10 years. Your quest will take you through quite a few towns and villages as you work to discover the cause, and confront it. However, the story and main quest stays generally very linear and simplistic, almost like it's an RPG for kids.
Along your route you'll meet some typically corny but cute and sometimes funny characters. Unfortunately, the dialog system is very simplistic, and there really isn't enough information told about (or by) the characters you meet, so it's hard to really feel a bond with them. It all feels very simplified, too, just like the main story.
Graphically, PoPoLoCrois is well done, featuring reasonably (if unremarkable) detailed and colorful artwork throughout. The animation is fairly crude, and there isn't quite enough variety in the scenery to keep it fresh as you play through. However, some of the cinematic cut-scenes are great.
Combat is turn based, and uses a very effective combination of free movement and a grid -- the grid is only used to direct attacks and spells, but your character can move dynamically about the grid before unleashing your attacks. Another JRPG staple -- level grinding -- makes its unwelcome appearance. To survive each new area, you need to spend quite a bit of time wandering around the previous level, fighting in random encounters. You'll fight many, many very easy battles, because without that leveling up, the next section will be much too hard. It's a poor (and monotonous) balance.
The game's music is nice, and fits the art style. There are very few sound effects, and only tiny bits of spoken dialog (usually when casting spells, so you get to hear the same bits of dialog over and over when you cast...).
Overall, there are more compelling RPG choices than PoPoLoCrois, but if you are hard up for a JRPG fix on your PSP, you could do... worse?