Halloween Kills is the best-reviewed sequel in the Halloween franchise, although its Rotten Tomatoes score still isn't all that impressive. The Halloween franchise has a difficult history with reviews, with the original 1978 movie being mostly critically lauded, but every sequel and reboot attempt getting panned. 2018's Halloween set things off on the right foot with a strong critical reception, like the original, but failure to retain that reception into additional installments has always been the franchise's struggle.
Rotten Tomatoes scores for movies released prior to the invention of Rotten Tomatoes may not be entirely fair for a variety of reasons, but they do provide a general look at a movie's reception, and the Halloween franchise has a bit of a checkered past. John Carpenter's original Halloween from 1978 still holds the highest Rotten Tomatoes score for the franchise at 96%, although many of those reviews were written in the last decade and don't capture the sentiment at the time of release. And while the film has always had positive reviews, it did have some notable detractors upon its initial release, but those issues have largely faded with time, which is one of the reasons Rotten Tomatoes scores for older movies may not accurately reflect the sentiment at release (unlike any modern release).
Regardless, following Carpenter's Halloween, a slew of additional Halloween movies were released in the intervening decades, all of which saw much more negative reviews, ranging from 9% (Halloween: The Curse of Michael Myers) to 52% (Halloween H20: 20 Years Later), with most landing under 30%. Even Rob Zombie's Halloween reboot attempt in 2007 (and its sequel in 2009) failed to garner a positive critical response. It wasn't until the 2018 Blumhouse Halloween movie that the franchise saw its second "Fresh" score at 79%. So far, its sequel Halloween Kills has 16 reviews, garnering a "Rotten" 56%, but that's still good enough to make it the third best-reviewed movie in the franchise. It's also still early enough to see that score climb since the number of reviews is so low that a handful of fresh reviews could swing it drastically - from its current standing it only needs two positive reviews to break into Fresh territory.
The horror genre is a bit odd when it comes to reviews and Rotten Tomatoes because audiences and critics aren't always in line, and even when both audiences and critics hate a movie, it may still perform well. This is clearly demonstrated by the Halloween franchise's nine failed attempts over the course of three decades to replicate the critical reception of the original, showing there's a level of demand there, even if they aren't getting the most positive reviews.
Whether Halloween Kills climbs into Fresh territory as more reviews come in remains to be seen, but it's not likely to impact the final chapter in the reboot trilogy, Halloween Ends, which is slated for release in October 2022. Halloween Ends was originally supposed to shoot simultaneously with Halloween Kills, but that didn't happen and it's now expected to start production in January 2022. Even if Halloween Kills winds up with mostly Rotten reviews, the franchise's history shows its reception shouldn't impact the production of Halloween Ends, particularly because of the low budget. Halloween 2018 reportedly cost $10-$15 to make and grossed over $250 million, meaning the franchise will likely continue to be review proof.