The Lancaster was a good bomber, but it should have gotten 0.50 caliber machine guns for defensive armament and should have used the Bristol Hercules radial engines instead of the more vulnerable Rolls-Royce Merlin engines. If the Lancaster had been built like that it’s likely a lot more RAF bomber crews would have returned, in my humble opinion.
Eventually several did get .50 caliber machine guns and one version did use the Bristol Hercules radial engine. But the Merlin engine was more reliable and was also used in several other aircraft, like the Hurricane, Spitfire and Mosquito .