Some say that the Commodore 64 was instrumental, along with other low cost personal computers, in the destruction and downfall of the gaming industry in the early 80s. While that may be partially true, I still remember that everyone I knew that owned a C64 didn't use it for anything but games. For us it wasn't about having a computer and heck my brother was the one who saved up his money and bought the system. What it was about was the games and the quality of games that was far superior to anything that was out at the time. Not to mention another thing that we did and every other C64 gamer at the time did, bootlegging games.
From what I remember, we actually only owned about 3 or 4 original C64 games; that being Leaderboard Golf, Batman, WWF Micro League Pro wrestling and maybe another one. But, we actually had hundreds of games. All we had to do was talk to a friend or a comic book store worker and request any game we knew about and we would have it a week later. This was because of the medium that the games were on, floppy discs. So all you had to do was put a piece of scotch tape on the side of the disc and you could write whatever you wanted on the discs. This, along with other Atari based licensing issues, is likely the reason why Nintendo was so insane about their games and keeping unauthorized companies from releasing games on their NES.
Design - The C64's design was somewhat lacking to me. While we never owned the actual Commodore monitor, we just hooked it up to our TV ala the Atari hookups, the rest of the system was large and bulky; not to mention heavy. The version we had came with a cartridge slot on the keyboard to play games, but it didn't work with Atari cartridges so to me it was worthless. The only game we had for the cartridge was Attack of the Mutant Camels. Another thing about the Commodore that really irked me was the loading time. I can't count how many times I had to wait 20+ minutes for a game to load just for it to have an error and have to reload it again.
Controllers - As for the controllers, you used the Atari controllers that you already had; which was a huge plus in my book. The best one that we owned was the Gemstick with the yellow button. The main issue was how hard some games were on the controllers. Playing Summer Games or Track and Field was brutal on a controller. To run you had to go left and right on the controller as fast as possible, which gradually wore on the controllers. Another little tidbit was that you could essentially use Genesis controllers with it was well, although that was pretty much pointless as no one is going to wait for the loading times nowadays. Using the standard controller port a the time was a great idea and I don't know why companies are so damn greedy now.
Library Strength - For Library Strength there are literally thousands of games out there (I actually can't find the real number anywhere). Every Atari game that exists was also on the C64, as well as a lot of the NES games before they were released on the console. I remember playing games like Gyruss and Spy vs Spy (There are 3 of em that I had) which led to me renting and playing them on the NES when I saw them. And because my brother knew a lot of people who owned Commodores, we could pretty much get our hands on any game we wanted.
Collect-ability - The collection factor of the C64 is hurt greatly because of it being a computer system. Being able to copy discs is great, but it gave us as gamers no reason to buy the games. The medium of the games being discs also hurts it as there is no easy way to display tons of floppy's. While, this does make the actual games worth a lot now, I still would rather find a NES or Atari game any day of the year.
Overall - The Commodore 64 was a really great system in the 80s to own, as it had graphically superior games to the consoles in the pre-NES era. The main problem was the loading times which greatly hurts the system now, as I'm more likely to just play a C64 rom then actually load it up on the old system. Using Atari controllers was great but some games took a toll on the controllers. Either way you look at it, the C64 is a great retro console and any true gamer should definitely check it out.
