I'd say he was the greatest keyboard player, all around musician, and 20th century composer.
Lucky Man was a Greg Lake guitar piece. Try Works Volume One.
I've been to hundreds of concerts in my day. Perhaps the best show I saw was the Carl Palmer Band at the house of blues in Vegas. Palmer and two teenagers played ELP music on guitar, bass, and drums. They had a mic out front and Palmaer got out from behind the drums between songs and did an interesting monologue, and he was very funny.
Emerson killed his career with booze and drugs. And his quality of life suffered greatly. He hardly ever performed in the past 30+ years.
I saw ELP at Soldiers Field in Chicago when I was in high school. For days ahead of the concert, the buzz was about how long and complicated it was to build their stage, which held a sizable orchestra.
He was missed all along, he deserved much better.