I had a late flight with AirCanada at 11:25pm a little less than a month ago. I got there around 10pm. I missed my flight because no one was at the counter to help me check in. (I actually don't know if that is AirCanada's negligence or McCarran's. If hiring ground service is specific to the airline and not the airport, then the airport gets 3/5 stars.) I tried to check in online throughout the day, but their site was down, so I had to go to the check in counters. The terminal was almost empty. The only people I can find was the TSA officers. I couldn't even find anyone at the information help desk. I'm only giving it one star because there was no wait at the TSA security checks, which didn't affect me anyways since I wasn't able to get my boarding pass.
Other than that, I liked how clean and new terminal 3 looked.