How is Guardians of the Galaxt riskier than a movie about, as near as I can tell, a bunch of green duck-faced blobs wearing turtle shells? Seriously, there's not way I'm seeing the new TMNT. The turtles themselves would send me running from the theater trying not to vomit. They're one of those things that don't translate well to photorealism.
Guardians of the Galaxy, in comparison, has been gotten insane amounts of advertising, quite a lot of interest, and most importantly, it's got the Marvel logo slapped across the poster. I'm not sure how anyone could look at it all and think it's risky. Out of the norm, yeah, but with Marvel's reputation, nothing they put out is risky.