The best part of the Volt was not having to get gas for about 9 months out the year, or only getting it once. You don't realize how much getting gas sucks until you do it every week (as I do now, since my Volt was totaled and I drive a gas-only car now). In the summer, I could make it to and from work twice without electricity. The car would run the engine at times even in the summer, just to run it.
Also, the lack of maintenance is great too. My VW Jetta Wagon needed regular maintenance, some of which was insanely expensive (the flush of the gear box was some ridiculous price like $600). The Volt rarely went into the shop for regular maintenance, maybe once every two years (though I had the car less than two years, and I never took it for maintenance).
Everyone thinks the tax incentives for these cars are great, but the Federal tax incentive is paid by taxes. What this means is if the car costs 70,000 (as Teslas can cost), or 40,000 (as a Chevy Volt can cost), you borrow that amount. At some point, you'll get the $7,500 off your taxes, but if you have a car loan, that amount does not lower the car loan.