It will be hard to put a finger on a sound for Van Gelder, because his career spans a period in which there was a revolution in recording technology, ranging from very FR and dynamically limited mono recordings to very fine stereo tape recordings that hold up to this day. But if you want a really good comparison you can find it in Miles Davis. In 1959, .Miles was anxious to move to Columbia, but had to fulfill his contract with Prestige; so anxious, that he did it all at basically the same time, recording what are now marketed as "The Legendary Prestige Sessions" with Van Gelder, with the same musicians (arguably the best band he ever had), in the same period of time in which he recorded Kind of Blue at Columbia with Teo Macero and Irving Townsend.
The comparison of the two is useful, but certainly not definitive, as the Prestige Sessions were recorded live, in studio. No overdubs, lots of mic bleed, few takes. Miles was in a hurry. Kind of Blue, by contrast, was carefully, slowly recorded by the standards of the day. Still, you can hear a lot of what Van Gelder was admired for -- warmth, presence, fabulous capture of horns -- and what he was criticized for -- a somewhat recessed sound, particularly on piano, and an overuse (not my opinion, but a popular one) of reverb.
Personally I think the Prestige Sessions are wonderful. When you consider how quickly and casually they were recorded, they transcend wonderful and make it all the way to how the hell did they pull that off?!?
If you want some serious contrast in Van Gelder's work, listen to "Birth of the Cool," then the "Prestige Sessions," then Cannonball's "Somethin' Else" or Coltrane's "A Love Supreme." Really, I don't know where the controversy is. To me, Van Glder was a giant who captured many of the best recordings of his generation.
Tim