Things I liked: Adjustable stock, weight and balance
Things I would have changed: A trouble shooting guide in the manual. Mine leaked air out of the barrel when I first tried to pump it up. Customer service (when they opened) quickly told me it's a simple problem to fix: Fill with high pressure air from a tank. Not having one, I slapped the buttstock and pumped some air with the gun cocked. Gun works fine now.
What others should know: I sighted the challenger in by locking it in a gun vise, firing 4 pellets and moving the sites to that spot. The problem I had was the pellets all went in the same hole, so I had to mark the 'grouping' with a sticker in order to see where I hit. Love it so far.