I agree with Jac. The Henschel's performances are terrifically nuanced - they fully inhabit the music and bring it to life like no other ensemble. The acoustics and engineering are excellent.
I have sampled every other ensemble that ever recorded the Mendelssohn string quartets (quite a time investment!). The Melos Quartet on the DG label (Mendelssohn Streichquartette Complete String Quartets was a close second for me, but I found them to be shrill at times. For me, the Henschel Quartet represents the high water mark for the Mendelssohn string quartets, where this amazing music meets its match in terms of sheer performance talent and engineering quality.