Guardians of the Galaxy (2014) is one of my all-time favourite Marvel films. I think it really helps that it is (semi) plausible- the special ‘powers’ people seem to possess coming from futuristic technology instead of some dormant biology or random mutation. It makes it possible – well, at least more possible than Marvel’s other protagonists and villains.
Other than the plausibility, Guardians of the Galaxy contains some genuinely funny moments, and the interactions between the wildly improbable and different characters makes an audience really root for the protagonists – especially since the villains (but a small handful) are faceless emotionless beings that not even the most empathetic of humans could relate to (this does beg the question of how they communicate with one another, or relay information to their leaders, but what more can you expect from Marvel villains?).
Ignoring some of the smallish flaws in plot though, the film has some stunning animation, a decent plot, and excellent actors. Even without watching any of the previous Marvel films, this actually works as a stand-alone film, making this truly a rare triple A film by Marvel that everyone needs to have seen.