I'm not keen on the Genesis 3-button controller either. The build quality, even speaking for the official Sega Mega Drive and Genesis 3-button controllers packed in with the systems, was all over the place. Some were acceptable, some were worse.
I can tolerate the 6-button, however.
Another problem on mushy d-pads, they make going straight left and right without accidentally pressing diagonally a chore. This is especially a problem for games where you need a precise discrete input in all eight directions, e.g. both traditional (Contra) as well as overhead run & guns (Shock Troopers), any game that uses "up" for jumping (lots of 2D fighters), hell even traditional Castlevania's method of using secondary weapons relies on a reliable 8-way pad.