The latest version of SimCity which was made practically unplayable since soon after its launch could have been avoided. Despite the publisher's claims that Internet connectivity is required for rendering portions of the game's content on Maxis' servers, players have found out the game does not require Internet access at all, at least not for single-player sessions. The company claimed that the game would require a "significant amount of engineering" to make it work offline.
As an experiment, a Kotaku gaming site player unplugged its network cable during a game session and was able to continue playing for almost 20 minutes before the game noticed the connection loss, clearly indicating that the game was not relying on the server to operate.
To further confirm that the game can played in single-player mode offline, a Reddit user "AzzerUK" claims to have been able to successfully mod the game to unlock a special debug mode that eliminates the checks for Internet connectivity altogether for game play apart from the ability to save the game, as the game can only be saved to the server.
Basically, it seems that the Internet connectivity requirement for single-player sessions is there for just one reason - DRM, a copy protection measure which had such a backlash that Amazon pulled the downloadable version of the game over thousands of 1-star reviews.
It would be interesting to see whether the experience for multi-player sessions would have been any better had single-player sessions not been dependant on a server connection, other than for let's say a once off activation after the game is installed and for periodic updates.