While it's always nice to get extra stories, in this case they come at the expense of the Guardians of the Galaxy story, which is only 10 pages in length. For a free comic book though, it's hard to complain about the length of the stories, especially if they are quality.
The GotG story opens with Tony Stark sitting with Corporal Flash Thompson and explaining to him who the GotG are. In essence, this short story serves as an introduction to who the GotG are, so for potential new readers, this is a perfect way to get started. Stark explains the background and origins of each member of the GotG in brief two-page summaries, adding footnotes about his time spent with them during the first six-issue arc of the currently ongoing GotG series by Brian Michael Bendis. Bendis also wrote this FCBD offering, which is penciled by Nick Bradshaw, and inked by Scott Hana..
The purposeful retelling of the Guardian's origins to Thompson serves as a set up for Stark asking him to represent Earth and join the GotG in their future adventures, which he does. We'll be seeing much more of Thompson, as Venom, in the pages of GotG in the months to come.
The second story is reprint fodder from the upcoming Thanos: The Infinity Revelation, drawn and written by Thanos' most famous handler, Jim Starlin. While there is only five pages of story here in this issue, the chance to see Starlin drawing Thanos again is reason enough to consider picking up this Original Graphic Novel when it goes on sale in August.
The final story (which is terribly out of place in this issue) is another reprint from an upcoming Marvel series, Spider-Verse. Early teasers for Spider-Verse have given an inkling that there will be many Spider-Men involved in this tale, and writer Dan Slott has mentioned in interviews that it will actually be EVERY Spider-Man ever, which is a huge expectation to live up to, because from the teaser art following the story, there are more Spider-Men than I had imagined. The story covered here involves a Spider-Man from an alternate reality acting out Shakespeare on a medieval stage before being killed. Written by Spider-Man architect Dan Slott, this story was penciled by Giuseppe Camuncoil and inked by John Dell.
Overall, this is a decent FCBD issue to put on your list, but if you are looking for an issue composed entirely of the Guardians of the Galaxy, sorry, that's not what Marvel is offering up. If you're a Guardians fan though, you'll want to read this so you can see how Venom is introduced into the GotG universe and how he came to join the team.