This is more of a 3.5, but I'm rounding it up for being an iconic Pittsburgh institution.
This has been my family's go-to pizza place for as long as we've been in Pittsburgh. Admittedly we went here on recommendation and never actually tried their primary competitor whose name I can never remember how to spell, so I can't directly compare. The pizza here has fairly generous portions of everything and the flavors are all what they should be (though the cheese was a bit too salty last time). The crust has a delicious doughy flavor. It's oily and the cheese can slide off, but that's all part of the appeal.
For whatever reason, after a few years of living in Chicago, the pizza somehow didn't quite taste as good as I remembered. Perhaps my taste adapted to the more cracker-like crust of Chicago-style thin crust, or the slightly reduced cheese levels on Chicago-style thin crust. (I literally only had deep dish twice; nobody actually eats those things.) But in any case, Mineo's is still very much a solid pizza choice.