If you're a casual Star Wars fan who just enjoys watching the movies without delving deeper into the backstory and lore of the universe, than this movie is great, and a very fun ride. It certainly outshines the prequels for a lot of people.
If you are someone who heavily reads into the entire story of Star Wars, than this movie disappoints in some regards. The main one is that they pretty much retold A New Hopes story for a new audience. While for some franchises that can be a good thing, for Star Wars it wasn't necessary. A New Hope stands up pretty well, and can still easily be enjoyed by a modern audience. This is supposed to be a continuation of the Star Wars saga, and not a reboot.
This movie could have had a very similar plot to it without the inclusion of Starkiller Base, they didn't need a superweapon for the story to work. The idea of a movie centering around finding Luke Skywalker is interesting enough without including a planet destroying weapon, especially when it has been done twice before.
Starkiller Base could have easily been just a key military base for the First Order. Rey could have still been captured and taken there, and the Resistance could have still launched an attack on the base to destroy it. Finn could have still gone there with Han to "lower the shields" and rescue Rey, and everything could have happened how it did.
The destruction of the Republic is another thing, why did it have to be done? The First Order really didn't accomplish much by doing it, especially now that Starkiller Base is destroyed. The planets that were part of the Republic aren't just going to join the First Order now, they'll probably just re-elect a new Chancellor and Senators, and support the Resistance a lot more. Don't try and tell me the Republic consisted of the 5 or so planets that were destroyed, because that would just be stupid.
I also doubt that the ENTIRE Republic fleet was just hanging out in orbit of it's capital instead of out protecting other systems that are part of it. I could believe that a good chunk of it has been taken out, but not all of it.
Say what you will about the prequels, but at least George Lucas tried to tell a new, different story than what was told in the originals.
A small part of me is concerned that with how much people are demanding the new movies be like the originals, and nothing like the prequels, that we're going to get 3 movies that basically retell the original trilogy's story. That would be a massive mistake in my opinion, we don't need a retelling of the originals, we need new, interesting stories in the Star Wars universe.
That said, I still consider 7 to be one of the best movies, even if it is just a rehash of A New Hope.
My current ranking is:
->Empire Strikes Back
->The Force Awakens
->Revenge of the Sith
->Return of the Jedi
->A Phantom Menace
->A New Hope
->Attack of the Clones