He runs out of MP too quickly, and has a habit of dying.... thats mostly why they are complaining.

In the PS1 version, I found osmose to very rarely get any MP back... making him very low on MP.. but in the GBA version, osmose seems to get huge numbers and he can refill his MP at will.
He still has horribly low HP and dies alot.. that is probably my only quam with him.