I was given SCBG as a gift one month ago and I find it quite fun once the rule comprehension is out of the way... However, each game so far has been dominated by the Protoss. Specifically, I haven't figured out how to stop a Protoss who masses splash damage with Reavers, Archons, and possibly High Templars casting Psionic Storm.
The Reavers are easy enough because they cannot hit air, and the High Templar depend on their support cards. However, I can't figure out how to effectively counter the Archons. They have high attack and health as well ground/flying splash damage on almost every combat card which is devastating . On top of that, they only cost 3 (2x1 + 1) gas so its relatively easy to produce one per build token allowing for them to be easily replaced as well.
The only thing I've really come up with so far is for a Zerg player to combine Ultralisks with Defilers casting Dark Swarm. That will neutralize both the Reavers and the Archons' attacks and still let the Zerg deal good damage to the Protoss. It's worth noting that Archons are immune to Queens casting Spawn Broodling (last I checked at least).
Terran players can take advantage of Science Vessels casting EMP Shockwave. However, even if the +3 attack kills the Archon, if the Archon has sufficient strength, that's two units the Terran is going to lose. 2 for 1 is not acceptable.