I haven't looked at the lost tales for a long time - I bought the first 4 volumes of HoME when first issued in paperback and struggled a bit with them (I was quite young) but completed the set when reissued and found a lot of the later volumes more approachable. Morgoths Ring is a favourite since it contains such gems as the Laws and Customs of the Eldar. I also enjoyed the History of LOTR volumes. I keep meaning to read them all systematically but I haven't settled down to it yet.

Far too tempting to dip in and see where the road takes me...
I can't help thinking that Tolkien was too much of a Niggle to ever finish to his satisfaction or indeed to that of all of his fans.... he would truly have needed the life of the Eldar