First playtest was rough. In building the cube I was so focused on making sure that there was sufficient enchantments that I didn't think to ensure sufficient creatures.
After some long discussion with the players, we diagnosed three primary problems with the cube, which I will attempt to resolve here:

• Magic has changed since 2013. Cards like Mantle of the Wolf and Archon of Sun's Grace, which seemed innocuous to me, were completely dominant and often immediately won games.
• There were not nearly enough creatures. 3/4 decks used out-of-synergy creatures just because they were the only creatures available.
• 5c Good Stuff trumped synergy decks hard. Due to the lack of creatures, the format was slow enough that the 5c deck could afford to wait a little bit and drop its bombs.

Solutions:

• The cube's power level is getting dialed back a bit to the general power of OG Theros' rares and mythics. Cards that win the game easily without the need for synergy are being replaced with cards that are just as powerful but still require synergy.
• As you can hopefully see, nearly every card being added is a creature. We're looking for something near 50% of the cards in the cube being creatures, if not that then at least 50% of the non-lands.
• We're now breaking singleton to allow the cube more flexibility. At the moment, this is only applying to the creatures in the scrying synergy. In addition, a number of god cards that weren't particularly synergistic have been replaced with more interesting variants.