Amusing enough, but without the visual flair of Edgar Wright to energise Pegg and Frost this too often comes across as self-indulgent and at other times just plain lame (the liberal sprinkling of dialogue lifted from genre favourites is a good example; occasionally it works, but no matter the talent of the performer, nothing can save the painfully naff inclusions of "Get away from her you bitch!” or "Boring conversation anyway").
The likes of Sigourney Weaver, Jason Bateman, Bill Hader and Kristen Wiig lend solid support and even the supremely talentless Seth Rogen is less annoying than usual by virtue of being present in voice-only (as the titular character). This is very much Pegg & Frost by numbers; what's the laziest genre to write for? A road movie. Check. What's the laziest way to attract a geek audience? Riff on your favourite sci-fi movies and cram your movie full of genre references. Check. Sprinkle on top lazy playing to the cheap seats with the abundance of cock/fart/anal penetration/bromance jokes and you have a fast food recipe for mediocrity.