A must stop place every time we visit Colorado is Casa Bonita in Denver. It is a ton of fun and always very busy. I've never experienced lines down the sidewalk (that I can remember), but it has happened to others visiting. The system for getting through the line and getting your food is fairly effective. However, it is crowded and not a great scenario for someone who is claustrophobic. I was getting more and more nervous as people were crowding around. Azure did great, but he was picking up on my nervousness and acting a little fidgety making sure I was OK. I think we were both relieved when we got to a place in the line we could leave the crowds and wait in the waiting area.
The best part of Casa Bonita is not the food. It is all the activity going on and all the places to explore. It is fun to walk behind the waterfall and get to look out and watch the shows (cliff divers, pirates, gorilla, etc). :) It is always great to be entertained while you are eating dinner and fun to walk around and check out shops, puppet shows, pinatas, etc. after dinner is over. I think the best part is putting up your flag at your table for your waitress to continue bringing sopapillas, refills, etc. :) If you are lucky, you can get serenaded at your table by a mariachi band. All in all, this is a must-stop on your Colorado vacation.