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Oh indeed - looks awesome :)

As for the limitation - if it is such a big problem that players can wall in enemies, why not let the enemies be able to punch through it slowly? Combined with having to have a digger/crafter go to fill the tile? Seems to be a good compromise between abusing the system and avoiding limiting it for the players overly much. :)
 
I hope that they'll make it so that the enemy can punch through it slowly but not teleport through it. If they do then I'll use it as a valid game mechanic and block up the tunnel that just exposed some level 50 boss mob and his minions until I have time to get my warriors trained up enough to take him on. If on the other hand they simply make it so that the enemy can also teleport through this block, then it's not likely that I'd bother building one in the tunnel to try to slow down the enemy.