Okay went ahead and played the shit out of this today. Built several different cities, and played through the whole game at max speed to get my city as large as possible within the 1hr limit.
I found that the size limitation was not as bad as I expected compared to the videos, but relative to previous SimCitys it was pretty constraining. While power gaming it at max speed I was able to fill the whole map within about 15minutes. The remaining 45minutes was spent basically just watching the city densify and adding services as needed to support the population growth. I know not everyone will be playing this like StarCraft with 150apm trying to complete your build as fast as possible, but that kind of becomes the mini-game with the one hour time limit on the beta. If you played through a bit more casually without the time constraint you'd probably get a lot more mileage out of it, but I think for serious gamers the small map size is really going to restrict the longevity of the game.
Below are some screenshots of my most recent 1hr playthrough, I was able to get a population of about 55,000 with most of the city at medium density (medium is the max density allowed in the beta).
Aside from the map size issue the game seemed quite polished. The interface and information overlays are all beautiful and intuitive. The agent system they use to simulate all the city systems is fantastic as well. Much more compelling than the simulation engines of the previous games. Being able to expand buildings and make some decisions about where to obtain resources (local vs neighbouring cities) are all nice features that add a bit of depth as well. The detail and graphics also seem quite good, assuming you are into the stylized theme and not looking for something photorealistic.
From the perspective of a fun sandbox you can casually play around in I think this game is going to be fantastic. On the other hand, if you are the kind of person who wants to min-max/power game it then I think you will find a lot to be desired. Even during my first play through I had no difficulty filling up the map with hundreds of thousands of dollars rolling in and happy sims across the board.