The picture quality is much better, but I don't think this was to be unexpected. Even on the DVDs you could tell the season had a completely different look to what came before. Coto's approach was to make this series feel like a true precursor to the original series and I think that's very much reflected in the way they shot on set. The first three seasons had more subdued lighting, muted colors and there's the use of soft filters. The fourth season goes for harder light, saturated colors and the soft filter is pretty much done away with (though I would have been amused if they had kept that for close up shots of women, ala TOS).
Just to give comparison, and these are from the DVDs.
Season 1:
Season 4: