The iMac is the exception to the rule of modern computing that no single model is unique enough or popular enough to match the fandom of groundbreaking '70s and '80s computers. Of course, that was Apple's point. When they released the iMac in 1998, they advertised its colorful body by criticizing the beige color of drab PCs. Today, Apple's moved away from the candy colored aesthetic for the iMac, but the computer's main draw remains unchanged. It's a simple, all-in-one design that incorporates all of the computer's components into the monitor housing. Easy to move, easy to set up.
The iMac was the beginning of a new era for Apple, which would usher in tremendous success with "i" products such as the iPod and iPhone. The iMac was never a massively successful product line -- Apple struck gold a few years later with its MacBook and MacBook Pro laptops -- but it was still the first Mac in years to make a dent in the Microsoft-dominated PC market of the 1990s.
The iMac also rebranded Apple as a style-conscious company worthy of imitation. In 1999, they sued a pair of computer companies for ripping off the iMac's look, which they'd promoted with a $100 million marketing campaign [source: McCarthy]. Given their success with virtually every product released since the iMac, that campaign was likely a worthy investment.