RHCP is extremely unchallenging in every way, but they're great.
If you like funk, listen to Mothers Milk or BSSM. If you can stand a little corny rapping, their first three albums are even better.
Their melodic stuff gets a lot of hate, but it's my favorite period in their work. By the Way and Stadium Arcadium both have a good bit of filler, but they are extremely awesome and guitar-melody driven. Oh, did I mention? You must learn to respect Frusciante as your lord and savior. Californication is my least favorite album, but it spawned their best singles. Otherside, Californication (the song), Road Trippin', and Parallel Universe are all great. Don't forget to check out the two tracks that were going to be a part of an unreleased album and were later included on their 2003 Greatest Hits: Save the Population and Fortune Faded. Both Fantastic.
Also, One Hot Minute is awesome. Just fucking awesome. John is a fantastic musician, but this album is actually my favorite of theirs because of the awesome collaboration between Kiedis and Dave Navarro of Jane's Addiction. Will Ferrell, their drummer, is at his best here, too.
And for John Frusciante's solo stuff, it's all good. If you're looking to get into it, check out Shadows Collide With People (basically the Chili Peppers without Kiedis), The Empyrean (lots of old school psychedelia), Inside of Emptiness (hard rockish), Curtains (sad-core, maybe), and The Will to Death (very late-60's rock sound, awesome lyricism).