Star Trek: The Next Generation is a great sequel to Star Trek. It has good characters as the original and good stories.
Star Trek: The Next Generation is a science fiction show with a heavy component based on drama. In my opinion, the science fiction elements are just the start engine and the spice used to create a developed stage to show the watcher how human behave in certain situations, like betrayal, love, prejudice, quest for power and many more. Some characters are even more good than the original, like Data, Laforge and Worf, but others don't follow the same steps. It has more important characters as well.
Overall the episode quality is good, but there are some episodes that drop the quality solidly. Fortunately they are just a minor part of the show.
I liked the original, but Star Trek: The Next Generation was the show that fully developed in me my liking for science fiction.
I don't like all the show aspects, but I like them enough to find it a great show.