If you don't normally use resource packs, too bad - this is required.
Not only was the map built with it, it uses modified textures for a
lot of features. The score, invisible walls, mob textures, books and
everything else - they'd look really awful with any other textures.
Heck, there are even some custom sounds!

Don't worry, though - SMP's Revival is a 16x16 pack, so no MCPatcher
is needed. It's also not very demanding from your system, so you
shouldn't get much lag from it. If lag is a problem, turn clouds off,
turn bobbing off, lower the smooth lighting, change fancy into fast
and heck, install Optifine.