How does one 'appreciate' Genesis?

If the melodies and instrumentation don't grab you there's not much else to "appreciate." SEBTP has been one of my favorite albums since I first heard it ~17 years ago, while Lamb, Foxtrot, and Cryme are all brilliant in their own right. If you can listen to Supper's Ready and not be in awe, they probably just aren't for you.

EDIT: I WOULD recommend giving Lamb a try, though. It's quite different from their earlier work, but it's hard to precisely explain why. For one, the tracks are shorter: there are no 10-20 minute "epics." However, while there are perhaps more songs that could be considered pop/accessible, it's also quite an arty, dense affair with a really hypnotic atmosphere and a fascinating concept that's perhaps the most engrossing ever conceived of in a rock context. There's a reason it's inspired book-length studies and massive online annotations. In a way, Lamb kinda exists in its own little universe, and I've known people who don't care much for Genesis but love Lamb, and those that love the earlier Genesis but dislike Lamb. I probably have a slight preference for earlier Genesis, but I can absolutely understand why many think Lamb their masterpiece and a work of genius. For me, I just find the music slightly less interesting than on their earlier releases. 

For one, I think it's important not to try to "push" your appreciation too much. It has to happen organically. I wouldn't say don't try to appreciate anything that you don't already appreciate, but I woulnd't do more than periodically playing whatever album(s) and just let the chips fall where they might.

There are two approaches that I think help:

One, immerse yourself in whatever it is for awhile. That works better for something that has a ton of works, though. For example, say that you don't currently appreciate 50s/60s jazz (the various bop styles) and you want to try to appreciate it. Well, if you ONLY listen to 50s/60s jazz for awhile, if you immerse yourself in it, that will help you start to appreciate it.

Two, just periodically give something a shot. Say once every 2-3 weeks, over the course of 2-3 years. That's a better approach for something like early Genesis, since there aren't that many albums.

It's important, I think, to listen while you're going about other business. Listen while you're hanging out with loved ones/friends. Listen while you're driving somewhere, etc. You'll be building associations with the music that make a difference.

At any rate, aside from Selling England by the Pound, my favorite Genesis is post-Gabriel, and aside from SEbtP and A Trick of the Tail, my favorite stuff is Duke through We Can't Dance.

I also like solo Peter Gabriel a lot--as well as solo Phil Collins. I like both more than I like most 70s Genesis. Not that I dislike 70s Genesis, but I just like that other stuff more.