As a lifelong LA native, clearly the number one complaint is traffic. In my last job, I had a five-hour round-trip daily commute to Orange County from Pasadena. Add in expensive tolls on the privately owned toll roads, the highest gas prices in the nation, and wear-and-tear on my vehicle, and it was simply a nightmare.
Public transportation is getting better — some people who live in the farthest reaches can take a Metrolink train and then perhaps a bus or light rail to work. However, these options don't really reach the majority of people who would like to use them.
Another downside is that housing prices are astronomical! Thankfully, I purchased my home 20 years ago — I would not be able to buy today nor afford to live in a relatively nice apartment in a desirable neighborhood.