It's like Minecraft Classic. The map is a 24x24 grass terrain. The only feature is breaking and placing blocks, with 61 blocks avaliable that you can change wit...
It's because in construct you can only use the CPU for calculating stuff, so having a good GPU doesn't mean almost anything. The raycast needs to check every single block in the game before drawing a single frame, that's the reason of the lag. And in fact, the game renders the double of the blocks you see, because the shadow is a object with transparent faces overlapping the model, not a texture or rendering tecnique.
Thanks for the explanation and good example.