I live in California and have been to Disneyland probably more than forty times. I have been to Disney World also, three times. We are about, this coming November, go on our first Disney cruise on the Disney Wonder.
Disneyland and Disney World are two completely different experiences. I don't think you can describe it was better or not as good. But I would say that Disneyland is like a slice of the whole pie if you are use to Disney World because it is so much smaller. With it being smaller, it is not as overwhelming. Within four/ five days you should, depending on how busy it is, feel like you have seen and done everything.
I think it is important to use Disneyland like it is suppose to be used...as a pedestrian park. The concept is that you never have to get in a car, bus or any mode on transportation to move around the resort grounds. So, staying on site, in one of the four hotels really augments your experience.
If you are staying for a longer period of time, I would suggest going to some of the other parks and activities the area has to offer. There is Knott's Berry farm (if your family likes roller coasters) about twenty minutes away and Legoland (about an hour and a half away). There is also Medival Times (which is a show and a dinner).
September is going to be a great time to go. The weather is warm and comfortable. I like going in October though because they really decorate to the hilt.
Have fun!