Was an unbelievable experience.
There are some frustrating aspects to the system---most of the trains sell out ahead of time, and you are assigned seats. If you get the three-seat side, you will have a more scenic view. The two-seat side is far less scenic. If you are more concerned about the scenic aspect, the first train of the day is not usually sold out. You trade fewer people for the haze of the morning, and your pictures won't be as crisp and clear. The conductor lets you move if there are empty seats, so if there are any you could scoot to the three-seat side before the trip starts.
There is no way I would have driven up the Peak. Too nerve-wracking. You see more wildlife on the train since it's on the backside of the mountain.
The observation center was not designed nor constructed to serve as many people as come up on the trains today. The center was extremely clean and well-run. There was a line for the food, but read the Cog Railway's website about the center and take heed of their tips for acquiring food when you get there.
You have 30 minutes at the summit. I didn't talk to anyone in my group who thought it should have been longer. After 20 minutes, I had to sit down and lay my head down for a while. I live at 60 feet above sea level and no matter how in shape you are, or how macho you think you are, you will experience some altitude sickness. It's nothing personal. Just go with it. There is an EMT who walks around and checks on everyone, and provides medical care when needed. We had a toddler in our group who needed hydration and oxygen and he was taken care of immediately and discretely. Listen to all the advice; it's a lot of information, but it is really, really important.
Everyone told us it "will be cold at the summit." It was 105 degrees in Louisiana the day we drove to Colorado and we couldn't process "cold." I bought a sweatshirt in the gift shop and was so grateful for it. Halfway up the mountain I needed something over my shirt. It was below freezing with the wind chill at the top and the wind was vicious.
Everyone in the Depot and on the train was friendly. The train was clean, the conductor was very informative. It may have seemed $$$, but we were willing to pay so we could enjoy the trip up and not have to worry about it.
If you are visiting Colorado Springs and want to see the mountain, next to hiking up, I think the Cog Railway is the best way to go. And yeah, I wouldn't go up in the winter. What's the point?