I'm not sure that Schumann is still under-rated. The more I dig around in this area the more fans I discover. As someone greatly interested in Schumann's works, I'd like to add a few comments:
For the symphonies, I consider the Sawallisch/Staatskapelle Dresden set the best of the lot. Next the Zinman/Tonhalle set. The Harnoncourt set is good too.
Schumann's many piano solo works are of course mostly outstanding. Based on a number of different versions that I have, I find the Ashkenazy boxed set as good as any. In one or two areas Richter is slightly better (eg Op 26), but there's usually a bit background noise, whereas the Ashkenazy set is very clean. Another superb interpretor is Horowitz (eg Ops 14, 19) . Rubinstein has a nice touch (eg Op 18). Other favourites include Berezovski, Le Sage, Thibaudet. My overall favourite piece is Op 17 Fantasie by Catherine Collard. These solo pieces, as a whole, are a match for anyone's!!!
The Piano Concerto has of course been recorded umpteen times, very often matched with the Grieg PC for some strange reason. My favourite version is by Murray Perahia/Sir Colin Davis. Another is by Curzon.
Dichterliebe. The recording by Fritz Wunderlich is superb. One of the best tenors ever.
Paradies und de Peri is an inspired work which Schumann was very proud of. My version is by Joshard Daus.
The Piano Quintet is one of the best chamber pieces in my opinion. I'd say the version by Argerich is the best.
Various orchestral pieces like Op 70, 73, 92, 134 are treasures worth seeking out. Versions with Murray Perahia are always very good.
There's a good overtures CD by Lior Shambadal that's worth getting.
The Cello Concerto is superb. In my view the Isserlis version slightly pips the Du Pre, but both are superb.
All the above works are of course well known. A less well known piece, which is truly wonderful, is the Violin Concerto WoO 23. My version of this is by Kremer, Ricardo Muti.
Yet another less well-known piece is the Mass, Op 147. The "offertorium" of this Mass is divine!
