Ok, so it's a bit of a con that you've got to shell out even more cash for this device but believe me, it really does make all the difference when it comes to playing VC games. The pad is basically a SNES joypad with analogue sticks. It's that simple. The d-pad is the same as that found on the Wii Remote, the GBA Micro and the Nintendo DS.
The build quality is what you'd expect from Nintendo - excellent. The design of the pad compliments the Wii Remote (nice clear plastic buttons for example) and the device sits snugly in your hands, just like the SNES pad did all those years ago. Playing games like Super Mario World is a joy - in fact it's the only way to play this game as the button layout is completely unsuited to your only other option - the Cube pad.
If you intend to take your VC gaming seriously then this really is an essential purchase. It's not going to break the bank either.