Every time I go into team slayer, I play Sword Base atleast 1/5 times. I don't get it either. I think it's one of the worst maps in Reach, slightly better then Pinnacle but only a bit.
The gameplay is always the same, get the shotgun and sword and camp at yellow lift. If the teams are a little bit balanced, the positions will switch 2 or 3 times in one match. It's just assoulting this smal part of the map.
When I look at my heathmap(
http://www.bungie.net/Stats/Reach/Heatmaps.aspx?player=Robbert014) , I can see exactly where the yellow lift area is, the other side of the map has nearly no colour at all.
I simply can't grasp the concept that people enjoy playing on Sword basea and I hope it gets the same treatment in Arena as pinnacle got.