He was an absolutely terrible character. The contrast with bit players like Jabba and Jango Fett (or even Zam Wesel) reveal how poorly thought out and executed this whole thing was. We never once get a sense of how Grievous thinks, or what his motives are. Is he just a fighter, does he have grudge against the Jedi, or does he really believe in the ideals of the CIS? Who knows. Is he enthusiastic about the violence, detached, or regretful? Again, no idea. Nor do we ever get any real information establishing how he's thought of in-universe. The only people we see obey him are robots, who are literally programmed to obey. Then he's openly disrespected by Anakin, which is the sort of banter we would largely expect that character to direct at his enemies. So where does that leave us? Was he revered by his troop? Feared by the Republic? Despised as a bumbling, incompetent leader? One too gun shy or too much a glory hog that disregarded the lives of his troops? Somewhere in-between? No clues here either. What about his skills? We literally never see him do anything that would qualify him as an exceptional warrior or strategist. Nor, to be fair, do we see him do things that would mark him as especially bad, either. He's just sort of their. He literally just takes up space onscreen. He's a crude, poorly written plot device with nothing memorable or exceptional about him at all. It's almost impressive the extent to which they went out of their way to avoid giving us any way to evaluate who this guy was or what he was supposed to be.