After playing twice now, I can say that I am really excited for the full game. Like others, I am still lightly concerned over the online/server issues but I agree with a lot of what what said already (remember diablo 3).
I have absolutely zero intention on playing in a multiplayer region.
I like the new way of delivering services, it is slightly more realistic in my opinion. It would have been nice to have some more transportation options though. I do think that getting to high density will create a bit of challenge with the budget while trying to balance all the services/taxes.
The way glassbox displays data is really neat and an improvement over earlier sim cities. I also think this game doesn't have the same goal as what sim city 4 has evolved into. Over time there will no doubt be expansions/dlc with piles of new buildings and I really hope its opened up to modding as well.
In terms of performance:
I maxed out the settings with AA on and it ran smooth as butter and looked great. The texture settings were on medium when I started and it looked a bit funny until I maxed it. My cpu wasn't even breaking a sweat.
I'm pretty sure that even with higher density it could handle a much larger map.
F.y.i specs are Windows 8, ivy bridge i5, 8gb 1600mhz DDR3, and sapphire 7870 OC running at 2048x1152.