I found ELP in a friend’s big sister’s record collection back in the 70s when I was about 12 or 13 and I loved them at that age. I bought a few of their albums second hand and still have lovely Island first pressings of Pictures and Tarkus. As others have said they never made a consistently good album, and to my mind they lack the creativity of say Yes or King Crimson, let alone Floyd, but they are good fun in a ridiculously excessive way. The side-long title-track of Tarkus has to be the high-watermark, it really is just bonkers (side 2 is dreadful, I think I only ever played it once!).
One day I’d like to hear Brain Salad Surgery again. I found a CD a while back and tried it, but it was some remix or something and sounded awful, just not how I remembered it at all. BSS is interesting as IIRC it features a Moog Apollo, which was kind of a prototype for the Polymoog and the world’s very first true polysynth.