Aiea Loop Trail used to be a pretty good ride until about four years ago. In a clockwise direction, the climb was worth the investment for the downhill but there are at least four spots where fallen trees require a complete dismount. The "flow" of what used to be a total blast is now ruined. If you're insistent on riding it, I'd opt for a mid-day ride during the week - the trail is popular with hikers on the weekends, which means said "flow" is further ruined because it's mandatory to yield to hikers.
I rode there alot back in 2001,and at that time it was in pretty good shape, the trail has a fun downhill section towards the end if you go clockwise. I left Oahu in 2002, so I really can't speak for the current state of the trail.
The way we ride today shapes mountain bike trail access tomorrow. -IMBA