He apparently had a co-writer on G2K and GFW. But yeah, while I also enjoy GvMGII and GxMG, there's no denying that his scripts all have some pretty outstanding flaws. Either he chokes under the pressure of tight deadlines or he's just not that good. I don't believe that the former is a great excuse, though: looking at GMK, for example, it's clear that better movies have been delivered on the same kind of schedule. He'd be better off if he killed half of his plot ideas and worked on other parts of his scripts. At that point, his output might become more respectable.
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