The L button and the D pad were optional for use. The L button usually had the same function as the Z button, and the D pad did the same thing as the stick. It was an alternative for the older gamers that didn't want to give up their D pads.
The gameplay on the N64 was epic. Graphics were acceptable for the time. Cartridges were better than discs as they can take a lot more abuse, also had little load time.