One attempt was James Delingpole's Coward series, I think there are three, they try very hard to emulate Flashman and fail.
GMF was a one off.
'Bunter Sahib' by Daniel Green wasn't bad, a stand alone novel about Billy's great grand father.
"Flashman in the Great War" was one I squandered pennies on unwisely; turgid, unbelievable, unamusing dross from beginning to end.
Delingpole's Coward series was more of an homage IMHO, and the first two were readable and relatively amusing, if a little OTT (I'd never heard of the third volume "Coward in the Woods" until you mentioned it which appears not to have been in print anywhere, probably with good reason).
Back to SF, Toby Frost's "Space Captain Smith" series started off well but lost momentum by the fourth book.
When it comes to genuinely funny SF comedies, there's not a great deal I can think of; Harry Harrison's Stainless Steel Rat series and the one off "Star Smashers of the Galaxy Rangers", Spider Robinson's "Callahan's Bar" stories, some of Scalzi's stuff, and that's about it off the top of my head.
Mention of Harry Harrison has reminded me of the Deathworld trilogy, a blinding series which I'm surprised Netflix hasn't snapped up the TV rights for and thrown millions at.