This is gonna sound really wacky, but I swear to God it's the truth: the only reason I was even remotely interested in watching "Showtime" was to see Eddie Murphy, Robert DeNiro, and William Shatner all working together in the same scene. I dunno why, but for some reason seeing this thespian trifecta working together was one of those once-in-a-lifetime deals that I never thought would ever happen in a million years. And I gotta admit, watching Shatner showing the other two guys how to be a T.V. action-show cop was pretty entertaining, and a nice bit of self-satire of his T.J. Hooker character. And yes, I DO need to get out more often, now that you mention it...
Other than the moments featuring the man formerly known as T.J. Hooker, however, I found "Showtime" to be a reasonably entertaining if rather ordinary spoof on reality shows. Eddie Murphy does his trademark smart@$$ routine here, which has gotten pretty old and stale over the last decade or so. And DeNiro probably did his part to fulfill some sorta contractual obligation. Fortunately, I've seen both leads do a lot worse in some of the other movie roles they've chosen over the last decade or so. But I've also seen 'em do better as well (DeNiro more so than Murphy). To boil it all down, "Showtime" had a few somewhat funny moments, a couple somewhat touching cute moments, and a somewhat fresh action scene (the bad guys' garbage truck hauling a police cruiser on its dumpster forks around the streets of downtown L.A.), but it ain't really all that different from other buddy-cop-action flicks that have come down the pike since the genre was born. Also, I didn't find it quite entertaining enough to be a "repeat viewer" type of movie.
Oh well, there's always "T.J. Hooker" reruns... heh.