Guild Wars 2 has pushed out mystery boxes for another event. Eugh. These are the worst things transferred from Asian MMOs and need to be buried in the history of godawful game design. It's bad value for consumers, exploitive, basically gambling and the opposite of fun. They were bad in Team Fortress 2, they are bad in dozens of asian MMOs and they are bad here.
Here's the deal item store games. I give you money for sensibly priced items, you give me lots of enticing products to get me to buy more. It's that simple. Planetside 2 might not have the greatest starting prices but deserves respect for it's 50% off weekly bundles, 50% off daily deal, triple station cash offers(!) and no god damn mystery boxes, temporary items or other gimmicks!
The only acceptable time for mystery boxes is when money isn't involved at any step.