Speaking as a (former) musician, the soundtrack did what it was suppose to do. While there's not many noticeable themes being replayed, most, if not ALL of the melodies present are completely new. "The scavenger" is a perfect example of this. Never heard anything like this in previous soundtracks. Trust me, I wouldn't have ever been a musician if it weren't' for the star wars soundtracks- I could literally point out what scene and dialogue happened based on the music alone once upon a time ago.
Sure, you're going to get your brief Imperial March quips, a few of Leia's theme in there, but take a step back and think about the context of the film. We have new characters, new entities being introduced. The prequels told the stories, for the most part of characters we already knew about- Anakin. I feel it was much more easy for John Williams to pull those same themes from the OT while crafting something new on top of it. To add, most of the Prequels "warranted" a more fanfare-esk type soundtrack. We saw larger battles, more action and much more Jedi.
I still even catch a few quips that were clearly in the prequel soundtracks, more specifically to Episode 3's
Episode 7? Not nearly as much action as we see in the prequels (not in this 1st of the 3 installments). The big fanfare's were present where it was needed- the "march of the Resistance" comes in when it needs to be- The moment the X-wings start to come in for air support at the battle of Maz's castle.
Something a lot of people outside of the music world don't seem to think about or take into consideration is that a musician's intentions is to convey a specific emotion through the composition. This is evident throughout the franchise, i.e., "memorable" themes that those who pay attention refer to. I can think of one particular, new variation of Leia's theme that was used for the last major TFA trailer (during the football game) and I can tell you that trailer w/ that specific theme damn near made me cry.
To sum it up, this soundtrack is geared to lead into the next films-not intended to be a domination of the film that people expected. This was intended to bring in new melodies not yet used for the Star Wars films. Yea, you can argue they're "not as memorable" but there's a lot of people who's expecting John Williams to come up with something "better" than anything we've heard with the OT soundtracks? Those themes are SO ingrained in all of us that it's not entirely reasonable to expect those to ever be topped by anything else as a result of our fandom. The fact is, these are all new. unexplored types of compositions. Williams's definitely went for a more subdued track this time, with the exception of a few tracks, which is almost opposite of all his previous works. I sincerely feel he wasn't trying to rely on the OT themes, only putting them where it was necessary- opening/ending credits, for specific KNOWN characters and for the Force.
That being said, to say this soundtrack is "garbage" is incredibly unwarranted and extremely ignorant. Just because it's "different" than what we're used to, doesn't make it any less valuable.