Entertaining but a little less than the sum of its' parts. Richard Lester's 1970s output is to my mind very underrated, classic adventure fair, from the physical comedy and pure adventure of his Musketeer films through to the superb Juggernaut, before he was vilified by nerds for Superman II.
This is the closest to a failure, sadly. His busy style
(especially the amount of movement in scenes and predilection for
bizarre period gadgets - how many other films feature a race between
prostitutes on stationary Penny Farthing bikes?) is perhaps not the best
fit with the books but the biggest problem is probably Malcolm McDowell.
I love McDowell and consider him one of the great underrated actors
but the problem is he's too good at playing the self-interested git side
of Flashman and not so convincing when the character's required to at
least appear decent and upstanding. A more heroic actor playing against
type (Oliver Reed, who appears as Otto von Bismarck, for example) might
have brought better overall results. Sadly this miscasting is hard to get away from, and even a string of inventive set pieces and lush location filming can't get around it.