Where I'm from originally we don't have Grimaldi's so I've never had it until I moved to Arizona.
There is something unique about Grimaldi's and how they do pizza. Is it the best pizza I've ever had? No. Is it a darn good pizza? Yes. I have had a few different options, my favorite being the white pizza.
My one gripe with Grimaldi's is the price, it is not even middle of the road in price - this may be one of the more expensive places I've ever had a pizza from.
I recommend this spot though, I've only been to the one in Old Town and it never disappoints in terms of taste and quality.