I'll tell you my experience with them.
In the summer of 1992, my arms room in Germany switched out 87 WWII era 1911s for new-in-cosmoline M-9s. I was the assistant armorer and I volunteered to do the bulk of the work to clean them up for issue. Furthermore, being in the position where I would have to sleep with my weapon in the field, and being able to pick pretty much whichever weapon I wanted, I took the pistol.
They feel great and shoot great. Probably not the best for people with small hands though. Particularly, the single action is very easy, and using military issue ammo, when it shoots, it pops right back down on target every time naturally. (I never tried any variety of other loads in one.)The controls are very natural and ergonomic.
However, as stated above, the frame is unforgiveably large for only being a 9mm/.40. Much bulkier than a 1911 in .45. The army should include night sights, but they don't generally. We started having problems with soldiers tampering with them, taking off the grip panels, removing the springs and putting them in backwards, dinging up the exposed mechanics, etc. These were NOT particularly accurate. (Although at least as accurate as the old 1911s with old bushings and barrels they replaced, and within the old and very low accuracy army standards for a sidearm.) Where any problem that I ever had with a 1911 could be fixed with a detail strip and parts replacement, every time something went wrong with an M9, I had to send it to support-level maintenence.
I also had a Taurus T-92, and while I liked the safety better, I had a lot of problems with it. Light firing pin strikes, the double-action was slipping for no explicable reason, I got rid of it.
It's not that the Beretta design is bad, it's mostly that there are so many other designs that are so much better. I don't think anyone can honestly say it is tougher than a Glock, A USP, or an XD. I THINK, that U.S. troops should carry the simplest, most idiot-proof, and cost-effective sidearm available. (Glock.) As for me, I tried a dozen other pistols for carry before I decided that real men carry 1911s. (Sarcasm intended, put your flame-throwers away.) It just feels better, shoots better, and carries better. (For me, anyway. I can tinker with it without destroying it. I WISH the army would let me take it to war, but I know it won't happen.