When I tested the game I enjoyed it so much I built two cities during my beta trial. I can say that the new SC will be a game and definitely a fun one, you'll probably find that the number of people who hold this view to be quite high. That is, if those people take into account the context of it being a game, and not a real strategy city planning and urban design simulator. Since the buildings and content were limited during the beta test, my best advice would be to hold out on pre-ordering the game, and to wait until it comes out and several 'lets play SC' come out.
When i played the beta, I was not restricted by any grid. I built a flowing city with a nice curvy roads along the beach and played the game how i wanted to. If you don't like the grid, that's fine; there is no grid in this game as it all just depends on your building style. I admit the size of the city is a bit small, but it can be lived with. As for the 'feel' of the game, it does not feel like SC4 at all to me. To me, SC4 became an arduous tool used to construct the perfect city or region - it simply was not a game to me - The new SC is definitely a game, one could say that comparing the two could be like comparing Operation and actual heart surgery. If you want a good game, I'd buy the new SC (when the prices drop and when mods are supported), if the size limitations are a deal breaker, you might want to consider the newer Cities XL.