Eighteen years seems like a strange milestone, but, whatever, I'll take any opportunity to honor one of the best home consoles ever made :)
The console itself is durable and reliable; the controller, though inefficiently shaped, allows amazing precision and control thanks to its analog stick; and the library, however small, includes some of the finest video games of all time. Nintendo struck gold twice in the area of 3D gaming, first with Super Mario 64 and then, two years later, Ocarina of Time, arguably the company's crowning achievement. Ocarina's sequel, Majora's Mask, was similarly great, surpassing its predecessor in several ways.
Nintendo also got a little help from its friends during the N64 days, most notably from British developer Rare, which reached a creative and technical peak during the fifth generation. Between 1996 and 2001, Rare released eleven N64 games, all of them good, some of them extraordinary. Rare proved its skill with action-platform games (Banjo-Kazooie, Donkey Kong 64, Banjo-Tooie, Conker's Bad Fur Day), racing games (Diddy Kong Racing, Mickey's Speedway USA), shooters (GoldenEye 007, Perfect Dark, Jet Force Gemini) and the odd action-puzzle game (Blast Corps).
In addition to Rare, several other studios supported the N64 with excellent games. These include Factor 5, LucasArts, Iguana Entertainment (several employees of which went on to found Retro Studios), AKI Corporation, Boss Game Studios, and Left Field Productions.
That being said, the N64 library was weak in a few areas. It had a dearth of RPGs and fighting games, especially when compared to its competitors' libraries. But its strength in other genres, famously platform, action-adventure, shooter, and racing, compensated for those gaps. In the end, despite some problems -- an unorthodox controller, Nintendo's reliance on antiquated cartridges, and the absence of high-profile role-playing and fighting games -- the N64 stands today as a shining example of 3D gaming done right, of developers pushing the technical and creative boundaries of video game design and producing, in the process, many of the medium's greatest games.