To start off, Denver International Airport or locally known as DIA is very different than any airport in the U.S. The check in, TSA check -point and baggage claim of all airlines is located in one medium size terminal: Jeppesen Terminal.
Here you can find Rental Car options, restaurants, etc...
And here is where you have to arrive to do the check in and to be picked up.
United is the main airline here, Southwest and Frontier are also the big bosses.
United offers plenty of room to check in with almost no-wait at all even if you fly in coach.
One of the great features is that in the TSA checkpoint there is a Pre-Clear line plus a Business/First Class/Premier line, which saved me at least 15 minutes.
After the TSA checkpoint you can proceed to your terminal.
You can walk or take the train if using terminal A.
And you must take the train (ONLY OPTION) to go to terminal C and B(United and US Airways only).
Of course I just visited terminal B, which is huge. And thankfully there are two well located United Clubs. But apart from that there aren't too many options. The only shops are the typically airport stores but it does have a lot of restaurants but only one Starbucks and it's not in the middle of the terminal.
This airport is good to say the least. Although because you do have to take the small train and walk a bit more, I would arrive at the airport at least 1 hour and 15 minutes before the flight.
But most important, it offers one thing that I think we all look at an airport:
(although it didn't worked on mobile devices)
"WALKING"(the least, the better): 3.7