The i3 we ended up with was a Mega World (base model) REX with heated seats. Really close to what I would consider, without the REX. I drove it to Roanoke from Charlottesville on the REX, Jess took it to work the next day (Troutville to Christiansburg on 81 with lots of hills), and we dropped it off on the way to Richmond that evening.
We're not going to buy one.

My thoughts:
The good:
The EPA rated 81 miles is pretty conservative. We never got to fully charge the darn thing because it takes 20 hours at 120V, but the guess-o-meter twice used up ~36 mi on a 40 mi trip that's mostly highway, and it was snowing and 27 deg that morning. If it had to do an 80 mi commute every day, I expect it would make it with 10 mi to spare.
It's fun to drive! It's nimble, surprisingly quick, and the narrow tires have plenty of grip for on-ramp action. It's really neat not having to shift or wait for it, it just goes. I can't say if it behaves at the limit, didn't get to autocross it.
It's comfortable enough and interior is pretty cool. Jess and I agree the ride reminded us most of a Mini, a little on the stiff side, and the seats are thin and firm, but it's great. The cloth and other materials feel like they'll last a long time. Visibility and spacious feel are excellent. Driving position is as good as any BMW (good). Lighting and little computer alert sounds are also cool.
The full-regen off-throttle (go pedal?) takes some getting used to, but I get it, and it's useful.
The bad:
Unfortunately the EPA rated 81 mi isn't wildly conservative. For us it doesn't leave enough headroom for any reasonable errands or getting stuck in traffic. And it wouldn't make it at all if the battery ages even 15%.
I would NOT CONSIDER the REX model. Not for a second. Nothing makes a $42k ELECTRIC CAR sound and feel dumber than hearing a 2 cyl motorcycle engine thrash about. You would laugh if you heard it from outside the car. And then you'd laugh harder hearing it from an i3 with it's blinkers on in the slow lane while it's struggling to sustain 50 MPH up a moderate hill. THAT really helps the brand. For the added $4k cost of the option, BMW should just include a used Accord. Or a motorcycle. Or a larger battery. Or put the REX on a little trailer with something larger than a 1.9 gallon tank.
The 120V charger is for emergencies only. And only for the kind of emergencies that leave you a few hours to sit around and wait. 4 miles of charge per hour is what I'd seen quoted elsewhere and is pretty accurate. This is just a limit of a 15A circuit, but really, if you needed juice and weren't within 10 mi of a charger, it'd be more realistic to call a tow truck.
I mentioned it's quick... but you get no sense (or satisfaction) of speed. It's like playing a driving sim, 30 and 60 mph feel the same. It's odd and I have to put it in the "bad" category. The car would have to go 0-60 in 3 sec before it felt impressive.
It's a little nervous on the highway and gets blown around by the wind due the short wheelbase, weight, and narrow tires. Better than a Mini, a hellovalot better than a 2002, but a little more active compared to anything else with a BMW badge made in the last 20 years. I'm fine with it but it's worth noting.
Climate control and stock stereo are not good. I couldn't keep my feet warm without making the cabin too hot despite much fiddling (I can't say I've ever had this issue in any other car), and the stock stereo in any base model rental car these days is better.
Traction control. Why can't I turn it off all the way? And why, after I navigate 3 menus deep to turn it "off" (mostly), does it reactivate itself when I use cruise control? I use cruise all the time, and I *never* want traction control, so this would bother me every day. Who decided these two unrelated things should be linked?
That brings me to iDrive, a poor excuse for a driver interface (not just an i3 thing). Once you get used to finding a few things, it's not horrible, but everything takes more time and more distraction that it needs to, and most features should be accessed only by a passenger. Pretty sure texting and driving isn't worse than trying to enter a destination Atari-high-score style or navigating contextual menus. Too bad you can't order one without it.
Another thing that may not be i3 only, I'm not sure, is that the turn signal doesn't actually click up or down into place. The 3-blink with mild press is great, but if you actually turn it on to stay on, it still returns to center and you have to push it the other way to turn it off. Why? Not a deal-breaker... but.... why?
Well, it was fun(ish) while it lasted, but we'll have to wait for the next generation or whatever Tesla may get around to making. Or an Elio. But I cannot justify the cost of the thing for my short commute, and it can't do the longer one.