A sad day indeed. Lennon, in my estimation, was a gifted, yet often cruel soul. The sum of all I've read leaves me with the impression that he was brilliant, petty, insightful, dark, lonely, and incredibly gifted.
I believe that with the Beatles he was greatly aided by the counterweight to his darker self provided by the other 3, and George Martin.
But what would the other 3 have been without him? No Strawberry Fields, In My Life, A Day In The Life, Girl, Norwegian Wood, I'm Only Sleeping- on and on.
How much poorer our musical lives would have been without him.
Just my opinion.