I am friends with someone who played for him (not in HOU), and he says Collins is a decent if humorless sort, not really volatile. He is intense/driven and has a lot of rules. He can have a good effect on a team at first, especially one that appears to need some organization and discipline. He is a sound baseball guy. BUT . . . the relentless pressure he keeps on his players causes things to go bad, eventually. My friend said he liked Collins at first, but by the end, like just about all his teammates, he wanted to kill hm.
That is pretty much how I remember him in Houston. In some ways, you could say he laid the groundwork for Dierker's success. I think it is Bill James, among others, who argued a strict manager like Collins can help a young, lackadaisical team initially; and by the same token, once a guy like Collins gets booted, a more laissez-faire type like Dierker can succeed, if for no other reason than the players are relieved to be out from under the thumb of the previous guy, and play well. Dime psychology, but there you go.