There seems to be some mixed reviews on this one.  I would say most perspectives cited below are right to some measure.  The music here is mostly marvelous period music-making (especially in the fast movements) from two top guns of the Baroque art - Manze and Podger.  But, as others note, some of the violin solos (especially in the slow movements) do not sound all that wonderfully lyrical and tonally rich - but somewhat 'strained' and lacking perfect intonation.  Perhaps it is partly due to the extremely close miking and over-projection of solo violins in the recording as others note below.  Another part if just the sharper and more direct style and sound of Andrew Manze - a more 'traditional' (gutty) period sound, if-you-will - which will not appeal to all.  If its a smooth, supremely-elegant tone you prefer, then the Grumiaux/Krebbers recording on Philips is probably the favored choice if you accept vibrato as fitting with Bach's music ... or the sensuous readings from period-violinist Fabio Biondi with the Europa Galante (my top pick).  Compare the Adagios of Manze and Biondi to see what is meant by "direct tone" versus "sensuous tone" due to the greater accentuation of vibrato, rubato and lyrical shaping of lines from Biondi.  A more humble yet warm and elegant version comes from the Kings's Consort with Elizabeth Wallfisch (Hyperion) if you prefer a more relaxed take on these works.