Good seats near the corner plate but only on the third deck of seats. "Upper reserved" is the official name I think, just a fancy way of saying nosebleeds. The biggest headache is getting there. There are ramps at various points throughout the ballpark that you must walk unless you want to take the stairs to get there.
I think the quickest way to enter this part of the stadium would be to enter thru Gate F and then follow the signage to the upper deck.
There are a few good eateries at the ballpark but nothing to write home about. Subway, Panda Express, TGI Fridays. Overall, compared to some of the other mlb ballparks I've visited, Chase Field is extremely underrated. Perhaps the most overrated I've been to is Kauffman Stadium in Kansas City. Aside from the fountains, they don't offer much.