I agree that the best thing is to return it to the store. Because if something is wrong with it they can give the heads up to the company and to other buyers. It could be a bad batch and other buyers would want to know.
I've had it slightly larger or smaller kibble, but not too much variation in size. The color has been different as well, though again there isn't too much variation. I've been buying it for about 5-6 months, now, and the quality has been pretty reliable for me. I've purchased everything from 5 pound bags right up to our current 30 pound bags.
With the fish formula you do get variations in smell, too. Sometimes the fishy smell is faint and other times it's very strong. Currently my dogs are on the sierra mountain (lamb) formula and the smell is pretty consistent.
Stephanie is right, a lot of things can account for kibble color and size.
I own a pet store, fed a lot of different foods, and sometimes different bags on a run can be different for all the reasons she's mentioned, and several more.
Now, here's my take as an owner -- if you're concerned, please bring it back. We don't get saddled with the bill, we're credited for the food. I have people who bring food back simply because they tried a new flavor/brand and the pet doesn't like it. :) (Now, please don't er, bring back open cans of cat food you've had sitting on your counter for two days (and scooped the cat food back in the cans from the bowls) because your cat didn't eat it. Really.
After two days in the summer, I don't believe I would eat it either. ;) Yes, I did take it back, but I was rather shocked. ;)
So, no, if you have any concerns about a food, take it back to the store, it's totally okay.
It sounds to me like a bad batch. The manufacturing company has records of which bags belong to which batch (day/time/ingredient distributors). If enough people return product from the same batch, that's when you get into recall issues. If the kibble was crumbly, then it was on the bottom of a pallet for too long. If your dog is fine with it, then perhaps it was an 'off' batch or they've changed something about the recipe.
But I agree with taking it back. The dog food gets destroyed and the store from which you bought it does not suffer any financial losses.