The Royals are lousy when it comes to watching a live game which gives fans even more of an incentive to watch the game from a good seat. 409 can be a good view as long as you don't sit too high up. Rows AA-WW are way up at the top, no obstructions, but I wouldn't sit in those rows even though the tickets are $5.
I've seen two or three games from section 409 and didn't hate my experience but the field box seats and even the plaza seats are ideal for a good viewing experience. The 400s are designed at an extremely steep incline which can probably be attributed to it's old design. Stadiums and arena designs and technology have grown by leaps and bounds since Kauffman's construction 30+ years ago.

Every seat in the Hy-vee level (top deck) is standard with a fair amount of room for your legs and a fair amount of room to put your items below your seat. There are no cup holders in the upper deck which I'm surprised wasn't part of the renovation a few seasons back.
The concourses in the upper deck are very wide, spacious and open aired which leads to good air flow. I just wish there was more than just Arrowhead Stadium and highways to look at outside of the stadium. Still, one of the nicest ballparks in the game!