At first I liked it a lot. I could be confident that the product we were building was worthwhile (unlike in engineering where I just had to take the PM's word for it).

But after a while I started to flounder. I couldn't figure out what we should build next and didn't know what to do. I had no training whatsoever. I tried to study PM methodologies but there are a million competing ones, a bit like self-help books. I don't really know how one becomes a good PM.

(Edit) To clarify I am no longer in this role. After that experience I've been working on creating my own startup, which is like SWE and PM combined, minus the salary.;-)