One application crashing will almost never take out the entire system or other applications. As for their user interface though, they obviously just threw the Windows 95 shell on top of NT 3.51, leaving numerous UI differences between the two. For example, NT 4 has a dial-up phone book app instead of a connections folder. Also, the security is a pain in the ass. Another thing that I don't like about NT is the way it keeps multiple desktops for each user.
Users get angry when the icons change.
They had to call me in to move the stuff between profiles. And the new user still wasn't happy because I hadn't set the same background and color scheme for them. Actually I think there may be a way for users to share a common desktop, but I haven't had a chance to try it. Windows NT 5 Haven't seen it. If you ask me, this whole web integration thing has got to stop.