Time to put on my fanboy gloves.
Firstly, about the linearity. It's FPS. It expect it not to be linear is to expect a dog to solve a maths problem. Some can, but it's a minority.
As for the Getting no where of Episode one, it was really more about Alyx and your relationship wiith her more then actually doing anything else. Throughout Half Life 2 and it's Episodes, it tries to build character and story. That's why I love it so. I guess if you didn't care for such things and rather a blood soaked gun frenzy that overlooks brilliant storytelling then I guess Halo or GoW would have been more to your liking.