The two car trains also apparently have no bathroom. Just an FYI, I know it's only a 25 min ride, but it is something I noticed.
I know you can't judge on the first day, but I expected it to be pretty full of people with free tickets and media, but when I rode it early afternoon the trains were mostly empty. Not that every train necessarily needs to be full, just an observation. Also a good portion of riders were actually going to/from the airport with luggage, I expected more people who were just riding it for fun since they gave all those free tickets.
The ride itself is very nice. The stations are beautiful (at least the terminal ones are). The train is quiet, smooth, large windows, and sometimes pretty fast. If that's how Diesel Multiple Units are, then I see no problem with DMUs, they work great.