These are early days for apps designed for the Apple Watch. There are quite a few good ones, but as developers are just starting to use an Apple Watch, it is no surprise that many Apple Watch apps need to go back to the drawing board. During a recent business trip in which a traveled on Delta Airlines, I tried out the Fly Delta app for the Apple Watch, and I was pleased to discover that it is very good. The developers did a great job of designing a useful app that has the info you need, but nothing else.
When you have an upcoming Delta flight, the app shows you in the center how much time you have until your flight departs. The bottom of the app shows you your flight number and your gate.

And that’s about it. The developers of the app could have included features such as a map of your current location, other flights you will be taking that day, frequent flier mile information, etc., but wisely chose not to do so. You can always use the Delta app on your iPhone for more detailed information, but when you are walking around the airport, the info you need is simple. You want to know how long you have until your next flight. You want to know your flight number, so that if there is an announcement or if you are reading a board you can determine which flight is yours. And you need to know the gate that you are walking to.
One of my favorite features of the Apple Watch is that it is so easy to lift your wrist and quickly look at key information, such as the time, the date, your next appointment, a text or email that just came in, who is calling you, etc. When you are in an airport, you are most likely to be focused mainly on the upcoming flight, so the info displayed by the Delta app is the most relevant info at that time.
In the Settings app on my Apple Watch, in General -> Activate on Wrist Raise -> Resume to, I always have my Apple Watch set to Last Used App. This means that when I am using an app, if I drop my hand to my side for a period of time and then lift my wrist again, I see the last app that I was using instead of going back to the watch face. This setting is perfect when used in connection with the Fly Delta Apple Watch app because when I lift my wrist in an airport, I would much rather see the Delta app with time to flight, flight number and gate number than see my normal watch face. And if I really do need to know the time, that is also on the top right corner of the Delta app. Thus, the Delta app functions as the perfect substitute watch face while I am traveling.
If you are actually on the plane, the Delta app instead shows you the info you would most likely want to see during your flight — how long until you land, and what gate will you land at.

When you land, the app welcomes you to your destination.

As much as I love the design of the Fly Delta app, there is room for improvement. First, instead of showing you how long until my flight leaves, it would be useful to have the option to instead see how long until my plane boards. That’s the actual time that I want to make sure that I am at the gate.
Also, there were times when the Apple Watch app got stuck and didn’t show me the correct time until my next flight … but then a few minutes later it would work again. And other times, I just got the generic screen indicating that the app was looking for information:

My guess is that this is not Delta’s fault but instead has to do with the way that Apple doesn’t currently allow native apps on the Apple Watch, so the apps instead have to work through the iPhone app, which can lead to a delay. Native apps should be out later this year, and when they are out hopefully this will go away.
Note that you also can use your Apple Watch as a boarding pass, but you do so using the Passbook app, not the Fly Delta app. Moreover, most every airline scanner screen that I see nowadays is a flat surface, which makes it easy to place your iPhone on it face down to scan a boarding pass from the iPhone Passbook app, but makes it incredibly awkward to use with a watch. You would have to twist your arm in a backwards position, or slip the watch so that the face was underneath your arm instead of on top of your arm. I can’t see using my Apple Watch as a boarding pass, so it makes sense to me that Delta did not include this feature in its Apple Watch app.
While there is room for improvement, I’m a big fan of the Delta Apple Watch app. When traveling, it is a great substitute for the normal watch face. When walking through an airport terminal, it is much easier to glance at my watch to confirm a gate number than to pull out an iPhone, unlock it, navigate to the Delta app and then locate that information. I hope we see more apps for the Apple Watch that use a single screen to show just what you need to know, and nothing else.