You order a marine to go around the building corner, and the moment he goes out of the corner, a shot from unexplored location is seen which kills the marine. Normal difficulty (There are like 3 difficulties more)
The original is much more complex in terms of details. For example its you who decide of
the layout of your bases and it is vital not only from economic viewpoint (some buildings are larger, some are not, so you have to manage free space) but if aliens attack your base the game generates an isometric map from your layout and comes into battle mode. The base is so perfectly mapped that even the smallest elements, like if you bought a five plasma guns and two magazines in general stores at that base, there *will be those 5 guns and two magazines as an item lying on that particular building floor at the map*. How crazy is that?
There's more and more.