It is a criticism you should have expected. From the very beginning of showing gameplay, they said that there would be story missions that are locked to a certain character. In a game like this, that rubs people the wrong way. Especially since certain characters are locked till later. It was a criticism that Fall of Cybertron received, and that was a generally better received game than this. In a game where you give the people the option to play their favorite character, it is generally best to let them do that as soon as possible.