Speaking as a GL fan, I don't think it was BAD, I think it was just....mishandled a bit. Tackling the first big leaps of Hal becoming a Lantern and everything is one thing, and even having those first inklings of him being able to beat yellow works too. Dealing with his personal issues is also fine. I think it's just the WAY they did those things really...doesn't work too well.
A large part of Hal's early time was training within the Corps. and later having to tag along with Sinestro, showing the differences in their ideologies and establishing things through that means. Parallax never entered the picture at that time. Using him was, frankly, a mistake. I understand that people might have not understood the concept of giant yellow space-bug of fear, but that's why you DON'T use him until you've gotten everything else set up that you can give proper time, attention, and explanation to his existence.
In short I think the biggest issue was they were trying to do too much. Too much of the wrong things and not enough of the right ones. It was a good attempt and it wasn't awful, but I have no desire to buy the DVD and put it on my shelf. They tried, but whoever was at the helm of this thing....I get the feeling they understood it, but they didn't care. They weren't all that much of a fan. Fans would have known better than to do what was done, I think.
