Unless your feeling nostalgic, there is little reason to play California Games.
Graphics: The graphics were never great. Everything was flat and cartoony, but in a stick-figure way rather than a cel-shaded way (of course, this was before motion-capture technology, let alone 3D that wouldn't come until the 64-bit systems). Even for the NES, the graphics weren't great. I like to compare every game to Ninja Gaiden (which would have been a 10). By comparison, this is mediocre.
Sound: Poor, even by NES standards. There are no special effects. When you crash your bike or skateboard, there is no sound. The music changes for each sport, but is the same recycled midi. The sound was just bad.
Gameplay: The game is entertaining, and that is really the goal of video games in general. There is enough variety to keep your attention, and it's challenging enough to tease you to practice a little more to beat your prior record. The ratings in surfing were one example where I kept going back to try to impress the judges and could never seem to get it above a certain score. You'll also do a lot of experimenting to see what tricks you can pull of in skating and footbag. So it is entertaining, you'd just rather be entertained by one of hundreds of other modern-day games that offer a little something more. For instance, when you pick your character, you need to pick your sponsor (from such greats as Ocean Pacific and Santa Cruz). But that's it, you pick a sponsor and play, there is nothing else about your sponsorship in the game. Quite simply, there is no depth.
I still pick up California Games every now and then, but it's purely for nostalgia. If you've never played before, you will likely never want to.