Mainly it's just that the plugins are buggy and undocumented, and everything requires a massive amount of intoning of unnecessary complexity before you figure out how to make it work the way you want, often manually. Its biggest failure is it's not designed to do things in an automated fashion, and it's overkill for what most people actually need to do: run some build scripts when someone commits something.

Thanks for the reply! I guess I wouldn’t fault Jenkins for poor plugin quality unless those plugins are supposed to be officially supported.