The premise of the Mystery content turned out to be very familiar me, thanks to other books I've read. In other words, I figured this one out, simply because the author was resorting to tricks and slight-of-writing that have been done to death--well, done to murder.
I went back to look at my updates at the Booklikes website, and did notice that I was still stumped as of page 153, but it wasn't long after that when a major penny dropped in my brain, and once a major revelation opened up before me--again, one that authors use repeatedly--almost everything formerly hidden fell into place. This disappointment--just about any whodunit I figure out is not going to get top marks from me--combined with rather cardboard characterizations, including the comic-relief ones, as the author focused on the puzzle and not the psychology of the people or the drama of the situation, brought the book down a bit, in my estimation.
Overall, not a bad effort. Was it Thomas Berger's catch-all quote, or someone else: "there was nothing really wrong with it, except that it was kind of lousy.". I can't even use that quote here, because the book was not lousy, just very, very familiar in its premise. I'm actually kicking myself for not noticing a rather routine bit of skullduggery (hah!) early on. The book is too short to really ever get dull, and the author sets a peppy pace, while running a handy formula with bits jiggled around. I would agree with Martin Edwards who, in his Intro to my edition of this novel, makes note of the fact that this reads a lot like a Freeman Wills Crofts novel, up to including the fact that Bude's detective, Meredith, is not much different than Crofts' (once-)famous Inspector French. That leads me to recommend the following Crofts novels, ahead of The Sussex Downs Murder:
Inspector French and the Sea Mystery
Inspector French and the Starvel Hollow Tragedy
The Mystery in the Channel
In particular, Sea Mystery shines best, if you want my two cents accumulated from any pennies that keep dropping in my head, from books that try and use Crofts' tricks to try and outdo him; and heck, they probably weren't even Crofts' tricks originally, were they?--a Conan Doyle novel comes to mind, and that's going way back, plus I think of a Michael Connelly Mystery that I loved, but that jiggles bits of a familiar premise.
I would say Sussex Downs Murder beats out Inspector French and the Box Office Murders which, to me, feels dated and quaint--though there's some nasty crap going on in that one thanks to ruthless villains--but other than that, I've given you my version of a reading order that supports the notion that Crofts jiggles familiar bits and pieces around more masterfully than perhaps Bude does. Still, I've read much more of Crofts, and should probably give Bude more chances to impress me. I certainly wouldn't be adverse to another John Bude outing...but he will need to stay away from that...that...um, that...that specific, um, thing writers do.