I read the first Flashman novel and stopped there, although I do have the second. I realise the covers are fairly similar, but I'm not really setting out with Flashman in mind.
To be honest, I felt that Flashman was a good novel slightly mis-sold. It seems to me to be a historical novel with a disreputable narrator rather than the absurd, bodice-ripping romp that the book jacket suggests it to be (essentially Blackadder's Captain Flasheart in novel form). To my mind it's dated somewhat, and Flashman is perhaps too low to be very sympathetic, even as an anti-hero. That said, as a historical novel, it's fast and entertaining. Just don't expect wall-to-wall japes.
I may read the others some day, but probably when and if I'm finished with Space Captain Smith. Out of interest, I've not read the Hitch-hiker's Guide to the Galaxy, either.
However, Fraser's war memoir, Quartered Safe Out Here, is an excellent book.