Ironically, 1553 IAH-ORD was delayed (only about 15 mins) this morning due to maintenance.
I say in 20L and would generally agree with the assessment of E+. It's certainly doable, but the narrow seats are noticeable (and the headphone jack took me forever to find!). One thing interesting about that particular seat was that it had 2 windows due to seating config, and the electronics were linked so they both dimmed together. This was frustrating, as I was trying to dim the forward window more so our row could see the entertainment, but this also meant obstructing my view from the window next to me. The electronic dimming also doesn't insulate from the sun completely, and the window can get quite hot in flight.
Good experience overall though, worth getting up early to take the flight and smell the new plane smell.