I guess there are many who disliked the tv series. As for the changing voice staff, certain voices seem to change with every movie, like Littlefoot.
There are some of the same voices from some of the movies and tv series though.
Looks like most of the folks have the same voices as some of the more recent movies.
Chomper as a different one then the 2nd and 5th movies, but that is to be expected since such a long time passed between those 2 movies and the tv series.
Mr. Clubtail has 2 different voice actors, guess they take turns, or use whoever is handy.