Mileage is not fixed, you can select the yearly allowed mileage anywhere from 10k to 25k, obviously with the higher mileage the higher the payment. Also of course you can build equity, if the vehicle that you have leased keeps it's value great, you can trade it at the end at what it's actually worth and not what you owe to the bank. I work for Chevy, so our mid-size Colorado is a great vehicle to lease, I have taken people out of lease as much as a year early by just taking the truck as a trade and not a lease-return, and they still at most times have equity in them. But then again, there are many cars that are the other way around, and even at the end you will be negative if you decide to trade or sell, so doing a lease-return is the way to go with a vehicle like that.
The horror stories that everyone has heard are no longer true, and leases are working better for the consumer.