Well we have no idea yet. Currently only registered Apple developers have access to it.
With that said, I can't imagine it'd be any worse than Yosemite. Of course, Apple are definitely focused on their future devices which of course, are by and large retina so don't expect any improvements either.
after nearly one week, how is your feeling regarding El Capitan on non-Retina MacBook Pros?
How does the San Francisco font look on non-Retina screens?