I’ve done about four rides now and here are my thoughts. I have a powertap so that is where the data is coming from and ride either rollers with some added resistance or a dumb trainer.
Setup and first update: Everything worked as expected. I would suggest that Ant+ choices stick. I like to use my speed and cadence sensor for cadence but I have to change it from my powertap every time. I think it would be good if it remembered your choices from last time.
Graphics: Really good. My son walked in the room and said it looked “laggy” but he is used to paying Xbox and Playstation games. I would say I wish it was just a bit smoother but that is probably my graphics card. It seems the road skips (very fast little skips) instead of rolling by. Also, I wish the deer and bear would run around and the wind generators are not set in places to optimize access to wind to generate electricity. 
I would also suggest that view 1 and 2 are too similar. I would replace one of them with view 9 except instead of being a 100 foot view make it about 30 feet - just far enough up so you can see the road ahead and at least one, maybe two, riders right behind you. It seems to me the views selection miss that sweetspot. 1 and 2 are too close and 9 is too far up and doesn’t allow you to see far enough ahead.
Odd Behavior: Three times when I started using the Join button my rider was facing the right way, swung around going the wrong way, and then no other players were listed and no AI riders were to be seen. I restarted each time and it fixed it. Not sure what was going on there.
Game Play and Comparison: I use TourDeGiro regularly and helped beta test it in 2012. As much as Zwift’s graphics is light years ahead of TDG, TDG’s game play is as far ahead of Zwift right now based on just four rides. My first three rides drafting on either AI riders or real riders was almost impossible. The behavior of the AI riders was sporadic and unpredictable. For example they would get in front of me then “jump” way ahead. In real life if a strong rider goes past me I can get on their wheel for at least a little bit, but in Zwift it was impossible for me to catch on to any rider until my fourth ride.
I will say my fourth ride was completely different. I was able to draft both real and AI riders a lot. The interaction with both seemed much more realistic and we even had several sprints between three people. I would still suggest there be some sort of visual cue, like a watts bar, showing the real time impact of drafting. Without a smart trainer there is no way to feel when the draft makes keeping up easier so there should be something visual that shows it. The “close the gap” message is nice, but a dedicated gauge would be better. However, even with this better experience I would say drafting, riding in a pack, and racing is more realistic (from a non-visual perspective) on TDG right now. I think Zwift’s graphics will pull people in but you need to have the rider interactions improved to keep people coming back.
.Fit Files and Strava Segments: It seems there may have been, or be, problems with .fit files. The reason I say this is looking at Strava segments there are multiple examples of low power numbers being faster than higher power numbers. You can randomly pick efforts of similar watts and “play” the comparison and see areas where one rider will speed up to ridiculously fast speeds that don’t relate to their watts. Unless people are having much better luck than I am drafting it is hard to see what would cause this considering that currently everyone’s weight is set to be the same. This is just on the Strava viewer/comparison feature so it may or may not relate to what happened in the game. I watched over 7 comparisons in Strava and saw riders “zoom away” without having significantly higher watts over and over and it didn’t seem to matter whether the comparison segment was the first lap in a ride or in the middle of the ride.
Riding in a Group: I know this is coming and there are probably already multiple planned features. I think a nice thing would be to have the ability to log onto a world and periodically have a button come up while you are riding allowing you to join a group about a minute before it starts (this of course assumes more than one person joins the scheduled group). You then get transported to the start line along with everyone else who wanted to (someone already mentioned a coffee shop so that would be a good place to be jumped to). That way you could just ride around until the start of a scheduled race or you could periodically join a group to ride together. If there isn’t a scheduled race maybe allow everyone to jump to the start line, if they want, on the hour.