The problem on the original is that they don't emphasize the important information pieces, all is printed in the same font style and size.
I agree with usaphp. With equal visual hierarchy, it's dismissing the fact that you care about some items 0% of the time and some items 100% of the time. And this difference between these states can change in minutes. For example, I don't care at all what my seat assignment is until I'm on the plane. I don't care at all what zone I'm boarding until I'm at the gate. I don't care at all what gate it says because gates change all the time. Even if I used mobile kiosk for check-in and it gives me a gate, there's a non-trivial chance that by the time I get to the terminal, that gate has changed. I do not rely on the gate assignment on my boarding pass, ever.
Similar items are not grouped when they should be: such as boarding time and gate.
And the font is not glance-able. It's a nice font that takes little width, but unless they start changing code share codes to "DL50,381,172", there's a ton of extra space that could be used. (of course whitespace is valuable too, but squishing information together for the sake of squishing it together is not a wise design decision.
Regarding someone's comment about color/shitty printers - this kind of design would require two designs: one b/w and one color. The strength of the reds and blues would take over the important information.