Surprisingly good.
Is billed as docu/soap rather than a comedy in listings so didn't expect it to be so funny, but all great TV has great script, execution, directing, production/editing etc. which all come together to appear so slick it seems effortless and they've nailed it with this.
The reportage style totally works as you feel you are observing real footage, and not sure if the 'lookalikes' themselves are accomplished actors/comedians who just happen to look like certain people (maybe someone on here knows), or they learned their art because of how they look, but they are all so good and you believe that 'De Niro' actually believes he is one and the same ("you looking at me?" to Stevie Wonder - love it) and 'Brent', whose whole character by Gervais is based around a socially inept manager who tries too hard to be funny, so isn't - being played by a lookalike who bombs by trying too hard to be him and funny is genius.
Inspiring.