Agree with Blade Runner, not so sure about Highlander. If we could only delete Highlander 2 and get a new one...

The Accountant, however, begs for one--it is written for one. When us writers create an IP, often we have a sequel of series in mind, and leave hooks in the story or underdeveloped plotlines--sometimes clues or hints or character arcs begging for more. These bits and pieces, if left untended, leave the original story weaker than it could have been if they were fulfilled the first time around, and we know this, but we do this because without them, a proper sequel would not work. This is why many sequels /do/ fail, or are poor--because the original film was /not/ written with a series in mind.

Die Hard was one of my favorite examples for a long time. Alone, the movie is incredible. But mixed with Die Hard 2... ugh. I still don't like Die Hard 2, my memories of that film are so bad I can't will myself to watch it again. They made up for it with Die Hard 3, but the original wasn't written in a way to suggest there ever being a sequel. However, another big series for the day, Lethal Weapon, was slightly staged for a sequel with a fantastic character dynamic that only got better in later films. The bad sequels don't utilize these hooks to canonically fit themselves in the arcs--and sometimes it is impossible, and when that happens, you do something completely different, but it better be awesome; or maybe the source material is so far out there you do something extreme anyways like Wrath of Khan and enjoy how awesome it is.