I can see the downsides to Led Zep. The playfield is really barren of mechs and components, and some people crave those; even the fancy premium mech goes away for 90% of the time. It's a boring fan layout with a useless upper flipper, with only one shot which is overly difficult and barely even does anything. The gameplay has no big payoff moments, nothing like the destruction jackpot or even winning a monster battle or soul shard, every shot is like, yawn, now hit the next one. The voice work is phoned in.
The payoff of Led Zep is in the scoring - going deep into the song modes, and building up and firing off the Icarus multiplier, like you build your own destruction jackpot by doing that. But not everyone cares about building up scoring like that (see also criticism of the Star Wars multiplier), and if you don't, Led Zep is kinda dull and grindy.