IMO the Tilemap object has been the biggest letdown.
All it would need is just a few extra tweaks, and it could have been the ideal way for new and old users to create their levels. As it is, it's all but useless. After importing a tilemap sheet, it's just about impossible to see the correct tile without a magnify option. Also, as already mentioned, been able to select and move, copy etc is essential.
I can't see any of this happening for C2, but fingers crossed that C3 comes with a built-in level editor, or at the very least, an enhanced Tilemap object.