Well I've played VI, VII, a very small amount of VIII, IX, and X, and I only beat VII and X. The others, I gave up on at some point because they were boring to me.
Somehow, I haven't given up on this game. It's got some major issues, but I'm enjoying it enough to keep going, oddly.
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~Halo There is no Crane, only Scarecrow!
http://img195.imageshack.us/img195/3739/scarecrowq.jpg