Guardians of the Galaxy will have significant and expansive levels but most likely not an open world. Generally, most RPGs feature open worlds. The game didn't feature an open world in the trailer, but it gave some hints about what may be in store.
Eidos Montreal has been upfront about Guardians of the Galaxy's narrative. There will typically be a guide or force that keeps the player on the right path. It is unlikely that the game will feature an open world of the kind we have come to love, but it may feature a version of it.
The developer has squashed any hope of an open world but hasn't ultimately denied the possibility. As they have repeatedly stated, the narrative is at the heart of the game. Despite this, it wouldn't be best to get discouraged, as many games have an open-world component that is almost as good.
A large part of Dragon Age: Inquisition is the Hub-Worlds, where players can explore large areas and go anywhere they want. We assume that Guardians of the Galaxy falls under this category based on the many trailers.
In Marvel's Avengers, there are also Hub-Worlds. Hub-worlds are not ruled out in Marvel's Guardians of the Galaxy, but there is no confirmation yet. We will update this article when we receive a direct guarantee.
For more info on Marvel's Guardians of the Galaxy Game, check out Is Guardians of the Galaxy Multiplayer or Co op? on Pro Game Guides!