When science fiction is funny, it's as funny as anything funny is ever funny. For reference, see the best funny work of Douglas Adams, of Robert Sheckley, of Kurt Vonnegut, of Harry Harrison, of Harlan Ellison when he's in silly mode, and of Woody Allen when he did Sleeper.
When science fiction is so determined to strike comedy gold that it circles funny in frantic elliptical orbits, it may intersect funny multiple times in rapid succession at the same time that it runs the risk of exhausting the reader.
Case in point: The Sheriff of Yrnameer by Michael Rubens (Pantheon Books, $22.69), the saga of ne'er-do-well space rogue Cole, who runs into zombies, space anomalies, monsters and Bad Men (the capitalization deliberate) while on the run from a bounty hunter named Kenneth who wants to lay eggs in his brain. He gains the municipal office of the title just in time to find himself in the crosshairs of a villain named Runk.
Rubens is a veteran TV comedy writer whose credits include a stint working for Jon Stewart's The Daily Show and whose book comes with an admiring back-cover blurb from Stephen Colbert. It therefore follows that there is some awfully funny stuff here, including the interactions with Kenneth and the intermittent teasers about the Bad Men, whose numbers diminish due to various catastrophes even as they approach the peaceful village, and arrive just in time to set up a clever punchline.
But there's a problem with attempting nonstop funniness. It's been managed many times before, and it will be managed again, but sometimes the problem is not so much the funny part as the nonstop part. It all comes down to timing, and in Yrnameer, the pace is so frenetic, the desperation to get on to the next silly thing such an overwhelming consideration, that the jokes and the slapstick can start to hit the law of diminishing returns.
It needs to be said, though, that this is also a function of the vagaries of a reader's receptivity at any given moment, and that this reviewer's saturation point is not necessarily congruent to your own or even his own in a different mood. He got tired. But he acknowledges that your mileage may vary.