The Lego franchise of games has had a long and successful run. From Lego Racers to Lego Lord of the Rings it has been a series filled with great games and massive success but in recent years this has been more true than ever. Just look at this year. This year will see a Lego Chima game, Lego City Undercover and Lego Marvel Universe and all of them are likely to be great games which meet with a lot of praise and both critical and commercial success.
Last year also saw multiple Lego games in the shape of The Lord of the Rings and Lego Batman 2 and both were brilliant games. For many franchises, such as Guitar Hero and Tony Hawk's, this sort of release schedule led to over saturation and, ultimately, death. But I think this wasn't really due to having too many games released in their respected series, I think it was really due to a drop in quality with the games themselves.
The Lego games are filled with improvement, the Batman games are better than the Star Wars games The Lord of the Rings game is better than the Batman game and Lego City Undercover looks set to be the best Lego game yet. Whether it be the addition of voice acting, the use of open worlds or a Lego game not being based on a licence, there are always changes and improvements being made. Contrast this improvement with the drop in progress between Guitar Hero games and you can see that the problem with over saturation isn't actually over saturation, it's that the games just don't develop enough.
So long as the Lego games can continue to improve upon their own formula I'm more than happy for them to keep releasing more than one Lego game per year, especially when they look as awesome as Lego City Undercover or Lego Marvel Universe.