The idea that a monster is magically going to appear in front of my eyes at a set interval in time is ridiculous. It is an easy way of working around the stocking of monsters. For those who have never played Everquest a train is a large group of monsters which will chase a party until they die or exit the zone. The largest creator of trains is monsters spawning behind players. Another problem is downtime.
Downtime is unfun.
Thankfully Ultima Online and Asheron's Call downtime is only a few minutes at a time maximum. In Everquest downtime can range in excess of a half hour if you are a high level melee type. The problem here is that downtime, even only a few minutes of it, is not fun. Another problem is travel time. I do not mean to use this word as a slur or a slander.