Tallest building on the Strip and a pretty killer view.
The 360 degree view of the strip and downtown was beautiful, but with my fear of heights, was terrifying to say the least. When we went, it wasn't too crowded. We got to enjoy the observation deck as well as watch the rides from outside. I was in awe of everyone going on the rides; I definitely would not be able to make it on any of those.
If you're staying at the hotel, you can get up there for free. We booked a hotel on Hotwire and paid around $86 for one night (would have been $56 if we didn't do late checkout) and 3 of us got to go up for free ($54 value).
I personally don't think I'd ever pay $18 just to go up and not go on any rides. If I ever overcome my fear of heights, I'll run back to the Stratosphere, where they will hopefully accept me with open arms. In the meanwhile, it's one of those, "you've seen it once, you've seen it all" places.