Missed out on passholder previews last weekend, but was able to get a ride on the first train today, on the left side in the second car from the back.
The right side is preferable, given the new shed, screens in the tunnel, as well as the Nessie statue. But I found the audio better on the left side, likely because that is where the speakers are on both lift hills. As for smoothness, I judged the improvement as being minimal. Perhaps that is because of where I sat and/or due to the cold overnight temperatures, and I will be curious to see how the ride feels in other seats on warmer days.
Overall, I am happy BGW made the investments it did here, and I only wish Six Flags Great America would do the same with Demon.