Nearly zero contributions to world building? We actually got some insights into the formation of the Rebel Alliance in this movie! We learn that it wasn't just a single united happy alliance. We learned that they actually weren't so keen on military offensives. We also learned that there were also Rebels that were willing to fight dirty, and didn't hesitate to order assassinations or kill people for practical convenience (like rather having a confidential informant killed rather then captured). We learned some details about how the Death Star project came to be and who was involved beyond Tarkin.
We learned that the Rebels also occasionally repurposed Imperial droids and that they can be very effective and dangerous. (Certainly better than those Trade Federation remote operated ones)
It's okay to not like this movie. I wouldn't necessarily call it a brilliant masterpiece either. I don't think it would work without being part of Star Wars, but neither would Empire Strikes Back or Return of the Jedi - these movies don't have to reestablish the entire setting, they can build upon what was already there. That is fine. And it's not just "fan-service". I probably missed most of that stuff, except the obvious - like Star Destroyers, TIE Fighters and X-Wings.