I have a few issues with fates:

1) Zero skill.
2) The mechanic used to calculate your contribution seems out of whack. Take Coeurlclaw King. You can hit him once and get max exp. Many fates are like this.
3) Fates only really work in some zones since "everyone is doing it." I duo'd a fate the other day for 11 minutes and got 10k exp. That same exact fate when taken down with 20+ people in 45 seconds... still nets 10k exp.
4) The "tag the mob and you get experience" mechanic doesn't belong in fates. I understand why it is like that for regular mobs. But in fates? There should be no exp reward for killing the enemy. Just the aggregate reward at the end.
5) I wouldn't mind actually doing a dungeon for some exp (it seems to be pretty good). But, there is a serious lack of tanks. Maybe they are all off leveling on fates? :P