First impressions are everything. A well designed/efficient spawn is the first thing a player will see upon connecting to a server. Also, the community and staff are another big part of what makes a server great.
Personally, if I join a server where the players welcome me and are friendly/helpful, then I'm more likely to stay and play for a bit. On the flip side of that, if I join a server and in the first five minutes I see players screaming obscenities at each other, then I will likely make a quiet exit.
Furthermore, staff is a huge factor for me. If my ability to enjoy playing on a server is hindered by some dick mod/admin, then I usually just leave. As a server owner myself, I only grant moderator positions to people I know very well and trust completely. In my mind, the moderators/administrators represent the server and should attempt to make every player feel welcome. However I realize that on bigger servers, there may be some times when a moderator/administrator is swamped by requests for help and therefore does not have a lot of patience for newer people.
Sorry for the long post...was trying to get all my ideas out.
- Sheldrake :3