I've been watching it, but based on what I see in videos and on paper, I don't think it's different enough from the iM for my tastes.
We recently replaced my wife's car (Hyundai Elantra hatch) with a standard-issue, boring Corolla sedan. The iM never made our test-drive list, as she didn't like it.
Even if it were my decision (instead of just my "influence"), I don't know if we would've bothered driving the iM. I love having a hatchback, but I found the driver's seat area a bit snug/claustrophobic, even compared to its Corolla brother. Looking at the measurements of the new vehicle, I don't get the sense it'll feel much different.
For us, the deciding factors on our purchase were the expectation of Toyota reliability and the safety features, which were easily $1,500-2,000 add-ons with the competition.