We've used the city pass before and thought it was great! We bought it at our local costco and it was dirt cheap! It was like getting 2 or 3 of the attractions for free. We went to San Diego first and did Sea World and the Zoo. My kids loved both! We also bought tickets to Legoland and did that. Then we drove up and went to Knotts (didn't like it much cause the rides were really big and it was really crowded) and finally ended up at DL for the last 3 days! It was a great trip and I thought it was a really good price for the pass plus now it has changed and has something better than Knotts, Universal? There were no problems at all, we just followed the "rules"-don't tear the coupons out of the book!! When we got to DL, that was the only coupon we had to exchange (for the park hopper) and I just walked over and did it in the evening so we could skip the line in the morning.
We have made many trips to DL since then but my kids still talk about how much fun everything was. My advice would be to do DL last though because it is the best!