There is an acknowledgment in the game that the Guardians of the Galaxy are a team. However, the game will insist that the player only plays as Star-Lord, since he is the Guardians of the Galaxy's leader. So, no switching from Star-Lord.
As the game was being developed, there was some thought of letting players cycle through characters. Eidos Montreal, the developers of the game, chose not to let the player switch characters.
This news was revealed shortly after the game was announced. Guardians of the Galaxy's Senior Creative Director, Jean-François Dugas, said in an interview with IGN:
"We started to discuss different opportunities like multiplayer or co-op. But we were really looking at what Guardians of the Galaxy is, and it's all about those characters. It's all about colorful personalities clashing with each other and sometimes getting along. It's a mix of all these things, their qualities, their flaws. And we thought, 'It would be freaking awesome if you could be one of the Guardians and put you at the center of that to be surrounded by those characters.' And this is how it came to be."
Because of this, the game is more focused on tactics than on straight action. The developers wanted players to think about the actions of the Guardians and the consequences of each situation. It's a very strategic game.