The fact that Vince Clark's fundamental style didn't really change between his Yazoo work and Erasure's Wonderland, which consequently sounds wonderfully early '80s retro (it was released in 1985, but sounds like it was from about 3 years earlier), in a way that The Circus (released in 1986) doesn't quite.
Some of their b-sides were really rather gorgeous.
And seriously, who else would have thought of doing synthpop cover versions of The Hall of the Mountain King and The Good, The Bad, and The Ugly? Marvellous.
(I appear to lack an Erasure icon, so have a Martha Jones one instead.)