I had a pretty good time playing, even with the simple, linear gameplay.
However, at one point you get to a level where he enemies are just crushing you, and the only way youll be strong enough is to pay to upgrade your weapons and armor.
The game is not free, but after an hour or two, it will have the "freemium" feel. Be prepared to spend money to finish it. I, for one, wont be.
PS3 Gamer about Echo Prime, v1.1.01