The main problem is that they took a single-player game and forced an always-online aspect. You can't save & reload on your computer any more (goodbye wanton destruction, which a lot of people did fun). You have to rely on the fact EA will keep the servers running for longer than a few years. What happens when SimCity 6 comes? A lot of people still play the originals years later... I doubt they'll be able to now. Again, DRM ends up screwing the legitimate customers and the pirates will remove it and play it without any issues. Companies have yet to learn this, sadly.
That's just the biggest issue with the game so far. The removal/changes of other features (like terrain tool and smaller city sizes) just isn't right, but I could forgive that if the rest of the game brought more to the table.
I also wouldn't put too much weight on reviews.

They notoriously known for favoring even the crappiest of games just so developers/publishers don't attack them, especially if they seem praise a game too much. Even without the complaints of the online aspect, it seems a lot of fans of the older games aren't too happy with this new one.
Side note: I'm craving waffles.