The most important thing is that you will now have Edge and Christian added to your roster. Attack of the Fanboy also notes the following:
You will also get the following 2011 arenas added to WWE 2K15: Smackdown, Extreme Rules, Over the Limit, and Capitol Punishment.Arenas, by and large, don't do much for me. I wish they had given us some WCW-centric ones though with the WCW DLC Pack. It's always nice to have at least a WCW Monday Nitro arena in the game.
The cost is $9.99 for the "One More Match" DLC. You can buy the Showcase DLC Season Pass for $24.99. Two more Showcase DLCs will be released (Hall of Pain and Path of the Warrior) at $9.99 as well.
Since I already paid for the 2K Showcase Season Pass I will be downloading this when I get home from work tomorrow. I must admit it was a little odd having a WWE game without Edge in it.