Great gun, though the recoil began to irritate me after a while so I got a Glock 19 instead. I like the 23, but for me the 9mm is more accurate and faster to shoot. You can't go wrong with a 23 unless you are recoil sensitive........like me.
It's been awhile since I shot the .40 Glocks, and the recoil wasn't too bad...but I could not shoot them accurately at all. The G19, on the other hand, I can shoot it very well. I have heard some complain about the unsupported chambers on .40 cal Glocks, but I've heard very few real k-boom events, especially given how popular they are.
I'm conidering trading my G19 for a G23 for the caliber upgrade, but I'll have to see how well I can shoot them now.
I say, try the G23. If you don't shoot it well, get the G19. They are both great guns.
-David