It operates most closely to the OG Droid, vanilla ICS. You can transfer all your apps to is just like any other Android device you move to.
Battery life is mediocre on stock ROM. Flashing a ROM will do wonders.
Benefits:
-dev support, other phones have dev support, but nothing like for the Nexus. Just go look up some of the ROMs, so many to choose from. Did I mention JellyBean? Yeah we got JellyBean.
-Beautiful screen. I'm a "screen elitist" and the Nexus definitely has one of the best looking screens on ANY device.
-Did I mention dev support and flashing ROMs? Yeah, ROMs
-First to get new OS. Refer to my first point. Get it?
You love your Bionic, and I can see why, a very good device. Do you remember your OG Droid? I don't know about you, but my Nexus definitely reminds me of my first smartphone, the Droid. Vanilla Android OS, easily root, almost an endless amount of ROMs, and best of all, first go at any major update. If you're into rooting and ROMing, you'd be crazy NOT to consider a Nexus.
So I think I hit all your questions and even possibly sold you on the benefits. My next suggestion to you is to go to the store, find a friend with one, meet a stranger with one. Try it out and see if you like it. Like any phone available it has its drawbacks (battery life being one of them), but the advantages/positives far outweigh them. Get your hands on one and then make the decision to go with one or not.