Not so much "ruin" as "take the series in a new direction". Then again, the #1 thing I would do to change Other M would be adding first-person on-rails sections, with vehicle and turret sections following. Plus I want to see the authorization mechanic return in the next Metroid game (I didn't like the way Other M handled it, but I would rather see it re-tried than for the series to go back to the old ways). If we did get an old-school, "non-restricted" Metroid, it should be horror-themed IMO.
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Currently Playing - StarCraft: Brood War