Here is an excerpt from Gamespot's review of the original Mafia released in 2002:
"The most serious complaint that can be made about Mafia is that the city isn't as tightly integrated into the missions as it is in Grand Theft Auto III. Often, driving across the city is more of a mood-enhancing interactive cutscene than a gameplay element that poses an actual challenge. This is fine in the beginning, but by the time you've reached the halfway point, you may find yourself wishing that you could simply fast-forward through these parts. You're often free to deviate from the quickest path to your destination and go exploring, but unlike in Grand Theft Auto III, there's little reason to do so."
Source: http://www.gamespot.com/pc/action/mafia/review.html?om_act=convert&om_clk=gssummary&tag=summary;read-review
Fast forward to 2010 for GameSpot's review of Mafia 2:
"It's with this explorable world that Mafia II commits its most egregious crime, however: Empire City goes largely underutilized. As with almost any open-world game, you can make your own fun (get the cops on your tail and then engage in a shoot-out) and pursue a few side activities (collect Playboy magazines and view the centerfolds in all their naked glory). Otherwise, you simply move from one story mission to the next without following any tangents along the way. There are no side missions to take. You can sell vehicles, but there isn't much to do with the funds you earn. You can buy new clothing from the freaky-looking, unblinking shopkeeper, but there aren't a lot of outfits to pick up. You can buy guns, but because your enemies drop ammo and a healthy variety of weaponry, there's no reason to ever visit the weapon shop. You can pick up one of the pay phones marked on your minimap, but unless the mission demands it, there is never anyone to call. This is essentially a linear, story-focused game that happens to take place in a big, beautiful city that incessantly teases you with potential never brought to fruition."
http://www.gamespot.com/pc/action/mafia2/review.html?om_act=convert&om_clk=gssummary&tag=summary;read-review
Looks like not much has changed except the expectations for sand-box games to have at least 10 hours of side missions and challenges. Mafia 2 does not, henceforth the lower review.
I was tempted to pick up Mafia 2 because of my fond experience with Mafia, but I decided to replay Assassin's Creed 2 after beating it in December 2009. Up next is a hard playthrough of Starcraft 2, then a full evil playthrough of Fallout 3 to get all the achievments.
Hopefully when I am done, October will be around and Fable 3 or Assassin's Creed: Brotherhood will be out.