Depends on your location. Some states do not allow it for deer sized animals. How effective it is also depends on how big the deer are. Northern deer tend to be larger than southern ones, especially southwestern ones. And that's just the Whitetales, Mule deer are larger still.
No less an expert than Duncan Long believes the .223 is a very effective cartridge.
There is a vast difference between a rim fire .22 long rifle and the .223. The LR propels a soft lead 40-grain projectile at ~1200 fps. The standard .223 propels a 55-grain jacketed projectile at ~2800 fps. Since kinetic energy increases by the square of velocity, the .223 delivers a much larger punch to its target, approximately 10 times that of a .22 LR. Top it with a well-designed expanding Nosler or Hornady bullet and it is not a bad choice, especially for smaller shooters or those averse to heavy recoil.
Here in Missouri the .223 is now legal for deer, though for many years it was not, mostly because of a lack of knowledge of ballistics on the part of the people making the rules at the Missouri Conservation Commission.