Kudos to you for taking a 2nd listen, but sounds like you need a 3rd and maybe a 4th.
They are so versatile and have such a wide variety of songs, your critique falls very flat. Going to California relies on "one heavy riff" and goes nowhere? Rain Song? Since I've been Loving you? No Quarter? Over the Hills and Far Away? Dancing Days? What is and What should never be? Achilles Last Stand?
Led Zep live is where it's at anyway, because they were such an amazing BAND, who let each member explore and take leads where they wanted to go, and always experimented with their songs (but in a way true to the original ideas).
Right now listen to some of their "complete BBC recordings". Amazing versions of Communication Breakdown (several), Since I've been Loving You, Going to California (perfection), etc. Some really good stuff. Then listen to the Song Remains the Same live album, specifically: Rain Song (brilliantly beautiful. Page is a genius, and Plant's voice a wonder), Dazed and Confused (27 minutes, including snippet of hippie song "If you're Going to San Francisco", which they turn into mind blowing metal-psychedelic beauty), Since I've been Loving you.
No one will ever beat Led Zep. Ever.