All of the songs on the Star-Lord soundtrack refer to events in Peter's life or the plot of the game. For example, "Bit of Good (Bit of Bad)" at least describes what Peter wants to be, "The Darkness Inside" is obviously about the Promise (even including the line "Promises are yours to break"), "Solar Skies" could be applied to the Chitauri's kidnapping of Peter and the events immediately following it, "Ghost" describes how Peter and Drax still think about their lost loved ones and can't let them go, and "Zero to Hero," which plays right before the second assault on the Sacrosanct, outright describes Peter's character development throughout the game and his learning to stop running away from hard truths.
Examining some dice on Peter's desk in the dream sequences causes him to recall a game of "Caves & Creatures" where his bard character got three critical failures. Bards in Dungeons & Dragons are commonly support characters who use music to power up their allies, which is reflected in the game's Huddle mechanic where Peter can use his music to give himself and the other Guardians a power boost. Meanwhile, his failures in the tabletop game reflect his struggles to properly support the other Guardians throughout the story.
The songs in the Guardians films (at least the first one) have a heavy 70s bend. In contrast, the songs in this game have a more 80s bend to them. This makes sense as the Mixtape in the first film was inhereted from Peter's mom and thus would contain music she would like when she was younger while the Mixtape in the game was a birthday present Peter received and was recently released at the time he was kidnapped (the 80s) and thus would have music contemporary with Peter's childhood.
Why did Groot file the group's name as "Gardeners of the Galaxy"? Well, a gardener's work is to make sure that plants can grow safely, to remove any invasive plants or animal that might damage them, and to protect the flora from any bad weather... so being a garden's guardian. To Groot, the two words might as well be synonyms.
The Nova Corps, denizens of Knowhere and the countless others all seem to fall to the Promise - something that generally alleges the Matriarch will return their lost loved ones to them - rather easily and quickly. Then remember that there was a galaxy-spanning war a little over a decade ago that wiped out millions (the Nova Corps being reduced to just Richard Rider at one point) and would be recent memory for the vast majority of people; it's incredibly likely that a huge majority of the survivors lost someone during the conflict, and would easily, readily accept the possibility of getting their loved ones back.
Fridge Horror
Consider the crushing emotional blow it was for the Guardians and Nikki to reject their Promise and return to reality. Now consider that most of the universe went through that without properly processing it first.
Within the Collector’s Emporium, one of the displays contains a Brood Queen. By the time Peter takes a tour, however, the glass is broken and the case is empty. Peter simply mumbles about how “That’s not good” and moves on with his day, but X-Men fans are probably crapping themselves by now.
