I was at my local pusher's store today, and held one of the new S&W .22 AR's. It had the tactical rails, and was pretty nice. I actually bought one of the new 'Colt' (made by Walther in Germany...) "M4" .22s a couple of months ago, and I love it.
To me, I like the Colt better, as it has a metal (alloy) upper and lower, compared to the S&W's composite construction. I also like that the Colt just looked/felt more like a real AR, including having a flashider and forward assist. The Smith did not have either feature. Even though the Colt's forward assist is non-functional, at least it looks functional... I did like that the Smith's slide release lever was functional vs. the Colt's that is just on there for looks.
I also liked the Smith's barrel, compared to the Colt's. The Colt barrel is a sleeved arrangement, and the Smith looked like it was regular/full metal barrel. This being said, the Smith did feel very light, but I assume that's because of the amount of composite construction... Even with the 'sleeved' barrel on the Colt, I don't think it really matters because it's a .22; plus it shoots very accurately, and lot's of fun! My Colt definitely did not function well with Remington Thunderbolts, but did not miss a beat with other .22 ammo that I had on hand. I have not tried this yet, but you can also adjust the bolt spring tension to 'dial-in' different types of ammo. I'm sure the Smith .22 is also big fun, too.
So, long story short, the Smith was nice, but for me, I'm happy to have the Colt. BTW, I own a real S&W M&P 15, and Colt ARs, and I like both, but the Colt's are tops on that list, too... These .22s are definitely not full-on versions of the real thing, but I don't think they're 'junk,' either. In my opinion it's worth the $$, others may disagree, but I think it's a fun ride for under $600...
Hope this helps for those of you considering one of these new AR .22s. I have not seen the new Sig .22 version; anyone else seen one yet...?