Editorial: The Problem With Sequels.
Here's the problem with sequels. Eventually, you will outstay your welcome.
Usually round about the number 'four', sometimes earlier. This is true of films more than books, and books more than video games, with TV series occupying some weird middle ground (if we think of series as progressive sequels), with some shows like Once Upon A Time feeling stale and worn out by the start of their third series, while others can get well into their thirtieth or fortieth series and still be reasonably fresh.
This is largely because the mechanics of sequels tend to be different.
With video games, sequels are almost never planned, but developers can be incredibly loose with what constitutes a sequel, and fans will usually quite happily let them do so. Totally new characters in a new setting in the same world with only somewhat similar gameplay and very little story connection? Sure! Totally new characters in a new setting in a completely different world with gameplay that isn't even slightly related, but there is kind of a shared aesthetic and recurring motifs? Hi, Final Fantasy.
With books, on the other hand, sequels are almost always planned, or at least prepared for - and without the constraints of budget, location, and actors, you can drastically change things between stories if you have to. If you need to have the main character age twenty years between books, that's totally fine, because you don't have a physical actor who has to have the terrible news broken just before you start applying the terrible BBC old person make-up.
With TV series, on the other hand, you're kind of required to keep a core cast, something made more difficult by the fact that your cast members will eventually want to leave, and you'll have to bring in new people to replace them - which is not even getting started on exhausting storylines, or worse, having a premise with a time limit built into it (I'm looking at you, Reign, because sooner or later you're going to have to address the total collapse of the historical basis for your show).
The TV series that tend to last are the ones that can constantly renew themselves. Soap operas, which are based more on location than people in a way, can maintain a consistent momentum despite a constantly changing cast. You're not really watching for the characters, you're watching for the scenarios they're dumped in, and the characters are only good for that until their storylines are completed. Doctor Who also does this in a much more literal fashion - the titular character literally renews himself every so often and turns into a new actor. This is so ingrained into the show now that quite often, the Doctor will regenerate even when the actor playing him has no particular desire to leave, just because it keeps the show fresh and allows it to make a clean shift from tone to tone.
Films are the most difficult. With films, you are faced with all of the same problems as television series, with the added issue that each film has to be somewhat self-contained. A film is a complete unit in a way that a television series simply isn't, and that means added rigmarole when it comes to sequels: Not only do you have to try to and scrape back as much of your cast as possible, deal with budget concerns, think of a fresh storyline, and deal with the fact that your premise may just not suit more than one film (hello, there, Taken, now approaching its third film as more and more members of Liam Neeson's family successively get kidnapped by unrelated groups, requiring Neeson to once again angrily growl down phones at people), but you also have to come up with a reason why the definitely-final-ending of your previous film wasn't definitely-final.
The other issue, especially with films, is expectation. This is a large part of why [Title Title 4: Subtitle] is a pretty deadly concept for most film franchises. We, as audiences, are primed towards trilogies. Three's a nice number. We like three. We're used to things coming in groups of three, and we're especially used to our entertainment coming in clumps of three. So, when somebody reveals that now there's going to be a fourth film, alarm bells start ringing, because isn't three enough? A trilogy is a complete unit, a cycle is just a complete unit plus one straggler clinging onto the edge, screaming.
This is not bolstered by the fact that fourth films tend to be pretty bad. Nobody points to The Phantom Menace as a prime example of the wonders of Star Wars. People don't talk much about Star Trek IV: The Voyage Home, and On Stranger Tides is the worst Pirates of the Caribbean by a nautical mile.
And that's why I'm not looking forward to Toy Story 4.