Seats in 420B will not let you down in any way. We did as good as we could have by sitting here, right behind home plate with the perfect panoramic of the entire field. The big video board is in straight away center field and it's huge and keeps fans informed the entire game with stats, replays and silly videos in between innings.
There isn't a bad seat that I've encountered although I hear the two bleacher sections next to the Mohegan Sun Sports Bar are pretty bad. For the 2nd largest MLB ballpark, navigation and sight lines are great all the way around. There are even sometimes no ushers in the upper deck which means fans can pretty much sit where they want. Our seats were really comfortable. Aisles were larger than the old Yankee Stadium.
There are many Yankees shops throughout the stadium too... on every level. Downstairs is the main shop that has everything a fan could want, and there is a separate shop just for female fans. Come prepared to spend more than retail price at the stadium, you're better off looking for Jersey outlets in the neighborhood surrounding the ballpark.