Each level has a number of different modes available, with
single - player only «classic» (standard tower defense) and «rescue» (sees you protecting a stream of vulnerable units); as well as «skirmish» (where your base pumps out units that head straight for the enemy's base whilst you must still defend your own), «capture the
flag» (where you build a special unit to capture a
flag) and «territory» (where you try to dominate by «
painting» as much of the landscape as possible).
On the one hand his five
paintings, including the famous Green Target and White
Flag, are perhaps the strongest
single body of work in the show, but on the other, one suspects Johns was the only artist not to be represented with a recent work because it is a fashionable position to assume only his early nark counts.