I must admit at first I wasn't expecting much when I booked the tickets online to go up in the arch, but having done it I have to say I really enjoyed it and felt it was well worth it.
We went on a Monday afternoon and there was no queue at all so went straight to the top. There was only about 10 people up there so we could see out all the windows perfectly and enjoy the view from many different angles. My girlfriend and I had the lift to ourselves up and down so was very smooth and plenty of room, would have been a little tight with 5 in it though.
Great views, a good gift shop so support St. Louis and do this, you won't regret it