I got in on this a few months back. For the full price it's not worth it, but if you can snag a membership whenever they run those "buy ___ game get GCU membership for $30" deals it's really worth it. You get a 20% discount on new games (which applies to any wrapped game, brings $60 games down to $48, and also stacks on top of sale prices), 10% extra on trades (which stacks with whatever other promos they're running), and other offers throughout the year. Using a rolling trade-in combined with the $10 BB Rewards pre-order certificates, I've paid a total of around $64 out of pocket for the following games (all of which except COD gained/gains you a $10 pre-order RW certificate):
Shadow of Mordor (which I paid for with some initial game trades)
Sunset Overdrive
COD: AW
Halo MCC
Far Cry 4
GTA V
If you like to play/trade and not hang on to stuff, you'll pay very little out of pocket. Good deal, thumbs up.