When you look back at surprise TV hits from the 1990s, 3rd Rock From the Sun has to be near the top of that list. It’s the story of four offbeat aliens who take human form and settle down in Ohio to research humanity. The cast featured legends like John Lithgow and Jane Curtin, alongside fresh faces such as Kristen Johnston, French Stewart, and a young Joseph Gordon-Levitt. The over-the-top antics of the aliens combined with Stooge-like physical comedy made the series a hit for six seasons. But all good things must come to an end, and sometimes that’s for the best. Here’s five reasons it should have ended when it did, and five reasons it could have gone on.

RIGHT TIME: Joseph Gordon-Levitt Was On His Way Out

Tommy Solomon was a key member of the crew on the mission to Earth. The youngest member of the family, the alien that inhabited the body of Tommy was the oldest member of the team by far. Joseph Gordon-Levitt played the character brilliantly, growing up on screen as Tommy did. But JGL was only on the final season in a part-time capacity, as he had decided to leave acting behind and go to university. When key actors start moving on late in a series, it’s often time to call it quits.

TOO SOON: Alien Introductions

One of the most surprising things about 3rd Rock From the Sun is how few other aliens showed up outside of the Solomons. A small number of associates from their home planet popped up, including their leader The Big Giant Head, played by William Shatner.

John Cleese had an epic recurring character as the representative of another species of alien that served as a thorn in Dick Solomon’s side. A cadre of model aliens from Venus essentially tried to rob Earth. Still, it seems like there were a lot of missed opportunities to bring a wider array of intergalactic characters to Ohio.

RIGHT TIME: The Sally/Don Relationship

As the mission’s security officer, Sally Solomon took on the task of being a woman and studying what that experience on Earth would be like. At first, Sally was resistant to the role, but soon fell in love with her new life. Part of her mission involved Don Orville, a local police officer that Sally had feelings for. Their on-again, off-again relationship followed a very standard sitcom pattern that had diminishing returns the longer the series went on. By the time 3rd Rock came to an end, the Sally/Don relationship just wasn’t interesting anymore.

TOO SOON: Strange Final Moments

Two different versions of the final scene of the last episode were shot. There was a version designed to give the producers an opening for a season seven if they got to make one. They did not. The version that aired sent the aliens back to their planet, leaving Dick’s beloved Mary Albright behind.

In a rather hurried moment, Dick erased Mary’s memories of him. This makes no sense, as everyone else they both know will remember him, and will think Mary is crazy for not remembering Dick. A longer run might have helped work out this moment more clearly.

RIGHT TIME: It Was A Really Long Mission

The whole point of The Big Giant Head sending Dick Solomon and his team to Earth was to perform a reconnaissance mission. Instead, they ended up hanging around Ohio for six years. Each episode featured a new lesson learned about humanity in the most awkward way possible. There’s a lot to learn about humanity, but it’s really weird that The Big Giant Head let things go on as long as he did. He abruptly called them back at the end of season six, though the reason for stopping the mission made about as much sense as letting it go on.

TOO SOON: Mary Just Found Out

The number of humans who discovered the true identities of the aliens can be counted on one hand. The big one was Mary Albright, who found out just before the Solomons had to leave. There were a lot of potential stories to play out once Mary knew, as it cast her entire six-year relationship with Dick in an entirely new light.

Plus, her knowing Dick’s secret while dealing with their mutual friends who didn’t could have been incredibly amusing. It was a great jumping-off point for a lot of great stories and jokes.

RIGHT TIME: As Far As Some Subplots Could Go

After six years on the air, many of the recurring gags and subplots went as far as they could possibly ever be taken. The Sally/Don relationship is a prime example of this, but there are others. Harry and Vicki’s incredibly inappropriate ongoing off-putting relationship. Dick and his jealous vendetta against his arch-enemy, Dr. Vincent Strudwick. These plotlines and others had become less interesting in season six, which is why some had fallen by the wayside. But it was too late to move on effectively in a fashion fans would have gotten on board with.

TOO SOON: Too Few Alien Reveals

Out of the circle of people who tolerated the Solomons, aka what they called friends, Mary was the only one who knew the truth about them. While a lot of comedic potential was left on the table with the Mary reveal, even more was missed in reveals to other members of their extended family.

Don finding out that Sally was actually an alien would have breathed new life into their story. It was odd that six seasons into a  story about aliens hiding in plain sight that no one else knew what was really going on.

RIGHT TIME: A Stale Premise

The cartoonish actions of the Solomons combined with their neophyte view of the world was the basis for the comedy on 3rd Rock. But by the end of the series, they had been on Earth for several years. It became less and less believable that they would still be confused or befuddled by humanity anymore. The cartoonishness became less endearing and more ridiculous. At some point, the Solomons should have turned a corner, and started getting with the program on Earth.

While there were a lot of aspects of 3rd Rock From the Sun that were played out by the end of season six, the show still had potential for new and inventive stories. Changes to their relationships with their human friends could have generated some excellent comedy and growth. The finale felt rushed, and not like a natural point to stop the series. 3rd Rock is a first-ballot contender for new episodes. The aliens could return to Earth 20 years later to see how things have changed, and deal with the ramifications of the sudden disappearance of the Solomons when they left.