Honestly, it's best just to go by release date, with Eno. You start with either the first two Roxy albums or Here Come the Warm Jets, that way, and that's easily the best way to get the ball rolling.
If you manage to stick around until shit like Another Day on Earth, then you're a blind-as-hell but well-listened fan.
Here are the most important touchstones, as I see them (and, yes, I've spun his whole catalogue many times, over the years...and, yes, few of these albums are perfect--such is Eno):
Here Come the Warm Jets
No Pussyfooting
Taking Tiger Mountain (By Strategy)
Another Green World
Discreet Music
Ambient 1: Music for Airports
Apollo
After the Heat
Ambient 4: On Land
Thursday Afternoon
Wrong Way Up
77 Million Paintings