To expand, Windows NT was originally a microkernel system where all the drivers were in userspace. This is more stable but ended up being very slow. With NT 4, they started moving drivers into the kernel and it was really buggy in the beginning. It wasn’t until NT 4 SP3 that it was usable.

4.0 was my first exposure to NT - I used systems running 3.5 a few times, but not enough to have any real opinion on it. I did know there had been big architectural changes, but that was all. I have no difficulty believing 3.5 was better though.