I think the highlight of this disc is the #5 (op.10/1) sonata. Kovacevich is really in his element in the first movement, which is full of tension, drama and nervous energy, and in light of which the interpretation of the rest of the sonata falls into place. The performance #6 is a likeable performance of a very likeable minor sonata, though as often with the earlier sonatas I think I prefer Kempff. I won't comment on #7, because for some reason I'm not very fond of the piece.
I have mixed feelings about Kovacevich's Pastorale. The notes point out that the name "Pastorale" was given to the sonata by Beethoven's publisher, not by Beethoven himself. Kovacevich's interpretation sometimes sounds as though he is out to prove the publisher wrong, with (e.g.) cadences that sound oddly vehement in the first movement and an emphasis on the "modern" sound of the harmonies of the coda (I think) in the last movement. The problem for me is that there are very successful decidedly pastoral readings of the sonata out there (I think it's one of the best things in Kempff's complete set, for instance), and I'm not sure Kovacevich's reading adds up to a convincing alternative conception, if in fact that's what he's trying to do.
This might be contrasted to his recording of the Waldstein or Schubert D. 959, where he emphasizes the tensions and overall the darker side of these pieces, with oustanding results in my opinion.