To me, the huge advantage of the E3 over the E2 is access to the sample library, though I also think the organ sound is notably improved. Why did you switch from an E3 to an E2? I understand, E3 had no better pianos, but what advantage would the E2 have, if the E3 has the same pianos plus samples and better organ? Was it a cost decision or something else?
When I had the E3, I was never really wowed by it. Sure, the sample library was interesting, but I had little use for it, particularly given the extremely limited filter controls. Yes, the organ sound was better, and the pianos (both EP and AP) had more variety and detail, but the sound was somehow more "plasticky" to me. But the big downer was the interface. The E2 is a joy to use live. I have all my basic presets stored on A1 to A7 - right there in front of me - with A8 set up to control Minimax on my Plugiator via MIDI. I just love the fact there's a proper depth control for the effects, and the sweepable presence control is very useful.
With regard to the organ sound, the Numa Organ has a more authentic, though more muted/mellow, B3 sound; the E2 is much more in-yer-face. The percussion is lacking and the CV is a little over-baked, but for rock contexts it works well, and it makes me smile! I never really warmed to the E3's "improved" organ/rotary with adjustable leakage, as it was more polite without really feeling that much more authentic IMO. The E2's Wurli and Clav are as good as those in the E3, and the Rhodes samples are a little more grungy. Generally, the APs are very poor, although the number 5 Yamaha Grand and number 6 Steinway are usable at a pinch - but I would never play AP from any Electro unless it had the hammer action keyboard. And talking of action, I find the E2's much more playable than the E3's for some reason.
Price was a consideration. I picked up the NE2 73 for $750 (with gig bag) - that's a lot of fun for a relatively low outlay. For me to buy an E4 73, I'd have to spend $2.5k, and then pay another $300 for drawbars on top of that, as I can't cope with those buttons. And I certainly couldn't justify keeping the Numa as well, which is still a better organ IMO. And, unless Nord released new EP samples, I'd still not have a Rhodes which could challenge the latest Korg offerings, or even be any better than those in the MP6 or Numa Piano (though the Electro's do have more variety).