EMGs have a few things that make me really like them, especially in the studio vs live.
These are very broad stroke, EMG vs. passive statements:
-There's a sort of 'roll-off' in both the extreme high and low frequencies when compared to passives, almost like high/lowpass filters. The result is a tightened bottom-end and a smoothened top-end.
-The pick attack is accentuated and brought forward in a way, almost like a slight midrange shift. I perceive this as increased picking definition and more of a pronounced percussive quality.
-There's some inherent compression, partially due to the preamp design and partially due to the preamp's headroom limitations. Part of the 'EMG sound' is the internal preamp being clipped, and it's totally part of the design. Basically a really clean limiter (clipper, really) being driven hard. The end result is essentially a slightly less dynamic, slightly goosed signal.
This last part changes how the pickup feels, though, which is also a big part of what I like about EMGs (familiarity being the driving factor) - the amp's gain won't be as responsive to changes in pick attack (still achievable, just not with the same granular range between 0 and 10), but there is this kind of fun-to-play, almost bouncy quality to them.
That's not all to say that a bassy active like the 85 will be tighter than a Duncan Distortion, or that an A2 mag PAF-style passive won't have a smoother top end than an 81, or that a 57, -X series, or single coil wont have a greater dynamic range/more dynamic feel than the D-Activator, or etc... but that's what I've noticed over the years.