Also to spice up the game you can download for free modding tools to create your own levels and other mods.
I haven't tried them myself as I don't own the game but im a huge fan of modding and have in the past modded quite a few games.
Also this site seems to have alot of mods for the game.
I cant guarantee all of these mods will work or that they wont cause damage to the game but its worth a shot.
As i said mods change files of the game so can in some cases cause the game not to work, but if the game becomes unusable just uninstall it then reinstall a fresh copy.