The collectives worked best when they were completist, like the "Borg" or "Q" ones. The time travel one was (inevitably) missing quite a bit, as was the Klingon one. The alternate realities one was a great collection as was the captain's log.
I'd like to see another one eventually.
All the sets with the exception of the Q one (which was literally every Q episode ever) were fan voted episodes thus "Fan Collective"). StarTrek.com had a list of episodes that fans voted for, and the top 10 got selected.
There were some excpetions. The Alternate Reality set included all the MU episodes plus the top 10 other alternate reality timelines. The Captain's Log set included the favourite episode of each captain's actor plus the other top 10 episodes.