The six-episode first season features shining guest appearances by 1) Kate Winslet, 2) Ben Stiller, 3) Ross Kemp, 4) Samuel L. Jackson, 5) Les Dennis, and 6) Patrick Stewart. So far (I'm on episode 4), both regular cast and guests seem to be having a ball, which always shines through and enhances any performance.
What can I say ... yet another for your must-see lists. :-)
P.S. Peeking ahead via IMDB ... season two includes Orlando Bloom, David Bowie, Daniel Radcliffe, Diana Rigg, Warwick Davis, Ronnie Corbett, Stephen Fry, Ian McKellen, Germaine Greer, and Robert De Niro (and those are just the instant recognition names)