I've only seen The Cage through the lens of The Menagerie. I was grateful every time the episode took us back to the frame story of Spock's court martial because The Cage is some tedious stuff, man. Pike is unlikable (some of the more tedious episodes are bearable, I find, if only for Kirk's charm), it crawls at a snail's pace, and it has that same morality tale feel with the disfigured woman rendered beautiful by magic later echoed in Mudd's Women (which at least had Mudd and Kirk to get us through it, as well as some genuine pathos).
I can't complain about the effects or costumes, though, because the entire series is limited in that respect. But the pacing, acting, and writing, IMHO, are brutal.