Well, I went last night, and had an absolute blast...thanks to slimz for the very helpful tip on tickets still being available. I'll try to do a report as best I can...as usual, it will be choppy and random.
We got downtown at about 6:45, and parked on the street (free) at 17th and Walnut, which was about five blocks away. Easy walk to the Sprint Center, and all the restaurants and bars that were open looked full. (On the way out, we saw the Cigar Box's lounge singer outside of his lounge - YIKES).
Right after we crossed I-70, we saw a line forming...it was the line to get in. We got our tickets to Will Call and used sclam's advice to use the Oak Street entrance. Good move. Seriously, it's unbelievable how stupid people are. The line to get into the main entrance (on Grand) wrapped all the way around the block until the last people were standing right by people waiting in the Oak Street entrance (shown on in crude MS Paint illustration on left):

We got inside, and I took a lot of stairs to our horrible seats on the upper level. We both wanted beer, and I needed coffee, because I'm addicted. The first concession stand's coffee machine was broken (WTF?), but the one right next to it was supposedly working. I got the coffee, then waited for my wife to go to the bathroom. I then noticed that everyone at the first concession stand was white, and everyone at the second stand was black. Maybe charity groups volunteer? I don't know, but it looked really bad. And then my coffee was ice cold.

We went to our seats, which were directly behind the stage. It wouldn't have been as bad if all the lights and speakers didn't completely block our view of the jumbotron.
The crowd was a lot of preppy folks, a lot of white trash, and about 5% cowboys (I do not consider cowboys to be in the same group as white trash). Tons of hot chicks in their twenties, lots of teenage girls, lots of middle aged folks, a few in the 60 and up crowd.
Trisha Yearwood went first. My review:

Thankfully, she played about 5 songs and left.
Side note 1: The musicians in country bands are generally incredibly talented. You rarely hear a missed note, and when they're given freedom to do their thing, they can really play. The musicians in both bands were no exception.
Side note 2: Since this was only my second arena show in two years, there was a new annoying thing it seemed like everyone had to do constantly - take crappy pictures with their camera, then take crappy pictures with their camera phone, then text them to their friends, then call their friends, then take more crappy pictures. The girl next to me was trying to take pictures with her phone and camera at the same time, and her mom had brought a camcorder. It was very annoying for Trisha Yearwood, but not as noticeable for Garth since I was more into the show.
Then, Garth I haven't been to many arena type shows, because arena shows in my lifetime have pretty much sucked hard. I'll just say, it's difficult to imagine a better arena experience than the one Garth provides. He can connect to the audience. It's surreal to be standing in an arena seeing my wife jumping up and down screaming like a teenage girl, the teenage girl next to me jumping up and down and screaming like a teenage girl, and a couple in their sixties locking arms singing along to every song. His appeal is incredible (I mean, he's sold more records than Elvis). I've never been to a concert where the crowd was more deafening than the speakers. I don't think I've been in a louder arena for anything. (although Timmy Ellis' three to send it to OT vs. OU has to come close)
He went through most of his popular songs, and even though he was kind of losing his voice, he sounded good. He isn't incredibly talented, and has a good, not great voice, but damn, he just has something that makes people love him. Some of his songs I don't care for, but I didn't mind. I really like a couple of his songs, and I'm fascinated with the pedal steel guitar, so any band that features that gets bonus points from me. He made the crowd go nuts when he was starting to do a solo acoustic song, said, "Is this out of tune? It's no good then." He then gets a sharpie and signs the guitar, and gives it to a girl in the crowd who was having a birthday. Although kind of corny, it was still pretty cool. Kind of like most of the night.
The definite high point was "Friends in Low Places". Very cool to sing along with Garth on that song. His encore was a solo acoustic set where he talked about his influences and played some of their songs...I especially liked "Amarillo by Morning", during which his fiddle player joined him and did a great job. He finished with "Piano Man", which I think is kind of a crappy song and a boring way to end the night.
Overall, though, I give Garth an A. Great show. Go see him if you can ($25!!!)