“Dexter” had been running on creative fumes the past few seasons, and Sunday night’s series finale — despite its emotional flourishes — merely underscored that this was a series well past its expiration date. Some of the sloppiness in the finish was perhaps the biggest surprise, given how meticulous its serial-killer leading man usually is.

For starters (and be warned: SPOILERS lie ahead), the show took its time this season before finally settling on an antagonist for Dexter, played brilliantly, as always, by Michael C. Hall. But the notion of essentially giving him a spiritual twin — another killer, with similar appetites, born to the woman (Charlotte Rampling) who helped devise the vigilante “code” devised to constructively channel his homicidal tendencies — felt like a bit of a cheat.

Perhaps foremost, though, the series wore out its welcome with the various cartwheels performed surrounding the relationship between Dexter and his adopted sister, Deb (Jennifer Carpenter). Initially a key connection to humanity for Dexter, Deb went from doting sibling to woman with semi-incestuous crush on him, from hard-bitten cop to accomplice, albeit grudgingly and guiltily, in his murders.

Sunday’s finale — written by Scott Buck and Manny Coto, and directed by Steve Shill — brought closure to all of that, but in the most expedient way possible. And while one can appreciate that the police would be sympathetic toward Dexter essentially exacting vengeance against the man who shot his sister, it’s hard to envision a scenario where a suspect is fatally stabbed in the throat while in police custody and the cop who did it just walks away, no harm, no foul. The show’s set in Miami, not L.A., for crissakes.

The best part, arguably, dealt with Dexter’s internal struggle regarding whether it was possible for him to live a “normal” life, even if that meant fleeing the country with his girlfriend Hannah (Yvonne Strahovski), herself an accomplished killer; and his young son. Dexter’s ultimate choice might have had a certain poetry to it, but its backdrop — against the cleansing tide of a massive storm — felt a little too steeped in symbolism and melodrama. (One can also question whether Hannah is really an ideal guardian, given her background, but at this point, why quibble?)

At its best, “Dexter” set up engrossing cat-and-mouse games, pitting its eponymous antihero against killers every bit as determined and twisted as he was. Understandably, that level of narrative discipline proved difficult to maintain, which perhaps explains the Dexter-Deb contortions undertaken to compensate for it.

For Showtime, the series’ place in history is certainly secure — not only ranking as one of the pay channel’s first original hits, but the springboard that helped launch its Emmy-winning breakthrough “Homeland.” Dexter might have left behind “a trail of blood and body parts,” as the character observes in the finale, but TV-wise, the series cast a long shadow.

That said, it was long since time for the series itself to breathe its last. And in this case, that farewell came too late to feel satisfying — or merciful.