Reliability is, I think, going to be the biggest game changer followed by the abilities of drivers and engineers to manage the torque. On the tech' side we're likely to see a lot of tweaking on the rear end with different aero' solutions (like the "suspension blockers", "monkey seats", diffusers, etc.) and probably quite visible changes to front wings as they need to be dealt with in concert. I expect to see some quite visible changes in body shape of the Renault powered cars as they deal with their cooling issues.
As far as the fuel saving issue is concerned that is more in the hands of the engineers and technicians. Driving to instructions from pit wall to manage fuel has been part and parcel of motor sport for a long time now, so I'm not sure any of the current drivers have any real advantage over another in that regard. One only has to recall the nervousness on pit wall when Seb' kept pumping in fastest laps to nail lap records whilst leading from the front, or the team orders to team-mates to hold station and run to a delta. If anything that will be about the temperament and ability of individuals to follow instructions, so maybe we'll learn something about drivers from that point of view.
As for smoothness, that's a two edged sword. The cars are going to be very tricky in some track conditions with all that torque and less down-force so smoothness when that counts will be important. However, drivers will also need to handle the cars when they're "out of shape" and dancing around. We've been missing that sort of thing since 2008. I'm looking forward to the tetchy, lively cars testing drivers reactions like the old days coming back.
Oh, another positive IMHO is the noise. I don't need my ear drums blown out to enjoy a gig, it's the quality and variety of the sound that matters. We've had years of all the cars sounding almost the same screaming their heads off like banshees. For me the return of growling beasts that we can actually tell apart is a welcome change. If they just turn down the bloomin' commentators and stop them shouting all the time we'll be quids in.