The biggest problem was the move from practical to digital. 3 is perhaps my favorite of the sequels, if only for some decent in jokes. I like 4 for being different and some great moments. 5 isn't that bad, but you can tell they had only a 100 bucks to make the movie, it's ideas were actually pretty interesting with the genetic variations on the Graboids, and the Jamie Kennedy twist was pretty obvious. 3 to 5 also stopped taking them seriously as horror/monster movies, so it's hard for me to judge them on the same level, I just had fun with them. 2 tried to be serious like the first, and it just was boring.
My biggest problems with Aftershocks were, Grady is one of the most annoying characters in the series, and all the characters that could die, either died off screen or no time was spent for me to care. I cared more about Nestor dying in Tremors than anyone in 2. And nothing was as horrifying or Heartbreaking as Chang's death.