Oddly enough, for me, when I discovered IQ, Dark Matter was their latest album, and I was instantly hooked. Love "Harvest of Souls", despite having some clear "Supper's Ready" inspirations (though perhaps that why I grew to love it and the whole album when I first began my prog journey.
As it stands, I love DM, TSH, and Ever, but have had trouble getting into Subterranea, and Frequency, though their last two have been easier for me to digest/get into.
Over-all, I think I enjoy most of their albums to varying degrees, and I don't think they've mad a single out-right BAD album, though I haven't listened to the two Menel albums very much to form a big opinion on them.
-Marc.