99 Spirits introduces a unique new type of rpg. There are many good, as well as bad points to it.
First of, it is very extremist on difficulty, it is either really easy, or pretty hard. However the difficulty to it doesn't rely on lack of skill, it is mostly because of a low level. The game is pretty easy itself, but going too fast through it may cause it to be a headache. I remember that when I got to certain boss on my first playthough I had absolutely no skills or support from monsters, and I couldn't go back to catch more because I HAD to defeat the boss. Took me MANY tries to beat, so hear my advice ALWAYS be ready with a nice or decent "party".
Second, it is the gameplay itself, it can get really repetitive once you find all monsters of an area. And sometimes, when finding a monster for the first time, you have absolutely no idea what the monster is. Has anyone ever heard of a Torii? or a Naginata? Well it was the first time for me.
Also, there are some features of the game that are never explained to you, for example Starve and Food, the only thing these two do, is make your character move slower on the map the hungrier you are and viceversa, you can't die from starving though.
It has a very nice amount of characters, each different from the other (in the sense each NPC has her/his own personality). If something, I'd say this game is like a visual novel + a puzzle RPG style. In addition the soundtrack in the game is actually really good, but you might get tired of it as it will repeat itself several times on different areas (Same that happens with any song, the longer you hear it over and over, the more likely you'll start to hate it).
It is a very nice overall game, I don't really suggest it for its story, but for the experience of the game itself. And again, the game is easy to beat, but a little time consuming (especially if you want all achievements).
However, the game does fall short for the full price ($15). So if you can get it with discount or on a bundle, I'd say go for it. The best advice I can give you, is to try out the demo, that is the best way to tell if this game is or isn't for you.