With all due respect, you bought the wrong product. I just had some original Doritos last night and tasted the same since my childhood.
Unless they've got a generic in the same blue bag or a new product called "No Ranch" Doritos...they're the same I've bought for years, only with MUCH less seasoning(hardly any in fact) from top of the bag to the bottom.
The local Spartan store sells their own Ranch version...not as good as the name brand, but at least they're fairly well-seasoned.
Could have been a bad bag, don't know...others would have to chime in.
I've noticed quantity/quality shrinking across the board on a lot of products I've bought over the years, while the prices keep going up,up,up.