That's exactly what they made, remember its a DEMO
and you are forced to do the missions, if not ppl will play the demo and not buy the full game.
The first demo mission is irritating but the other missions are pretty good plus you get about 10mins in between each mission to mess about.
In the full game you can choose not to follow the story and just do the side missions.
But you gain more exp doing the story missions, the quickier you unlocky cooler abilities.
You have karma choices as well to make during the game so do you help the police or help the civilians or help your mates or help someone else.