I like the idea, but I think it is just a little too massive. You have way, way too much customization with your monsters, far more than you have over your main characters. Determining which stats to focus on, the thousands of different infusion possiblities, and combining that with the sheer number of availible monsters, makes the entire thing rather overwhelming.

I wish they had just removed the items from the process. Choosing which monsters to level, which to use, which to infuse, and when would have been enough. Giving them different items which provide different stat boosts just takes the entire system too far. Do I level this monster now, or wait until I can level specifically its magic stat? Should I keep this one on my team, or try to infuse it into a better one. Is this guy going to be awesome once maxed out, or is it going to be a waste of materials and infusions?

The system is just way too huge. I don't know what to do with it. Which is why, although I have captured every monster I have come across so far (and hunted out some of the rare ones, like the Exoray), I have yet to level up any of them.