Of the game's 500+ buildings, just under 200 are locked from the start, but nearly all of them were opened up after a mere 10-15 hours of casual play, so there's no huge barrier to what passes for progression in Societies.
In fact, that ease of entry is an important element of Societies, which is sure to pick up some fans from the same crowd that has made The Sims such an unabashed success. Yes, we're talking about the much-maligned casuals. Where SimCity proper required intense mental concentration to balance the many fronts of running a realistic city, Societies allows players to kick back and experiment with very little worry of their city heading in a direction they don't like or falling prey to a disaster... unless they summon one.
While that's a smart move for the franchise from a business stand point, it also severely limits the actual content packed into the game. There's enough fun to be had toying around with various society types to make the game worth a purchase, but the more you start placing the same buildings over and over again, the less interesting the game becomes.
Publisher EA's solution to this is commendable: power to the people. EA claims that Societies is the "most moddable SimCity ever." Whether or not that's true, though, it remains to be seen if Societies can pull in a dedicated enough community to keep new content coming. After all, the hardcore SimCity fanatics are unlikely to be pulled into this simplified game.