Keith Emerson nailed the synthesizer solo on "Lucky Man" in one take. Probably the culmination of the generally Throw It In recording that makes "Lucky Man" so impressive.
Karn Evil 9 is arguably the band at their best. In particular, there's the EPIC opening of 'First Impression, Part 2':
Welcome back my friends to the show that never ends
We're so glad you could attend, come inside, come inside
Generally, it's sometimes hard to believe that the incredibly loud, bombastic, complicated music they were famous for originated from only three guys.
There's something kind of awesome (not to mention a little bit heartwarming) about the rendition of Lucky Man from this concert (skip to about 49:15 if you want that particular song, though the whole concert is worth listening to). As Lake is singing, the entire audience joins in.