Anyone who says Mac isn't good for gaming is obviously pretty uninformed.
Just because one indie game out there doesn't support the same graphical shader type doesn't make an entire line of computers not capable of gaming.
Mac GPU architecture only supports one shader type, the one Blockland doesn't use. Most company produced games now-a-days support both shader types, so Macs can run them, however Blockland doesn't currently have this support, nor will it most likely ever.
Macs can run games just fine, it just so happens that it can't run Blockland after minimum because it just simply isn't supported, not that it can't handle it.