Genesis is my favorite band. I've been listening to them for the past 17 or so years. I own 11 or so of their albums. My favorite songs: The Fountain of Salmacis, Seven Stones, Turn it on Again, White Mountain, Dance on a Volcano, Looking for Someone.
In the 1970s, Genesis was one of the most technically skilled bands in history. They have since been outpaced by Dream Theater and the like, but that's more a factor of the progressive scene at large than any knock against the lads. ("Too many notes", anyway.) They were tight, balanced, adventurous, and unique, both with music and lyrics. No real band has ever sounded like Genesis (don't bother me with the Marillion argument- I don't hear more than a vague similarity). But after Peter left, yes, it did slowly start to turn into the Phil Collins show. Phil even covered a Genesis song (Behind the Lines) on one of his solo albums, and it was actually a better version, but it was downhill from there. It's a tribute to the greatness of the band that even their weakest albums could still produce both artistic and commercially superior material.
Their 1997 album (after Phil left) was embarrassing. It's such a disappointment, I actually cannot recall its name right now. Ah yes, Calling All Stations, that's it. Wish it hadn't come to mind, but there it is. The singer did his best, but he was just out of his depth, and Tony and Michael were apparently on autopilot. Oh, this reminds me, I have a special about the history of the band on my DVR which I haven't seen yet!