Nintendo isn't known for DLC, but they've been trying their hand at the sometimes controversial tactic recently. There are extra levels for New Super Mario Bros. 2 on the eShop, and there will likely be more expansions for future Nintendo titles. Being Nintendo's first Mario game on the Wii U, then, it isn't surprising they decided upon DLC for New Super Mario Bros. U.
While most video game DLC contains something trivial like new skins or extra guns, I would consider New Super Luigi U to be its own game instead. Since Nintendo will release it as a standalone disc later in 2013, it appears they feel the same way.
Throughout the series, playing as Luigi often affords noticeable gameplay differences from controlling his brother. In The Lost Levels, Luigi could jump higher and farther than Mario, but he slid all over the place, making precise jumps difficult. This formula was repeated with other Mario games where Luigi is a playable character. In New Super Luigi U, Luigi's slippery but more powerful style became incredibly frustrating when Luigi would slide off a pipe to his death, since I was so used to relying on Mario stopping on a dime. If you play long enough, though, you get used to it.
Look familiar? The scattered 8-bit Luigis did help me like Luigi U a little more.
The levels within New Super Luigi U also have 100-second timers as opposed to Mario's hundreds of seconds, supposedly in an attempt to rush you. At first this has the effect of "oh no, I need to finish," which causes mistakes and a few deaths, yet that feeling leaves when you discover how short each level is. Because this is just a $20 expansion, it isn't surprising you can complete it quickly, but it ruins the point of having little time to finish a stage. Still, I found Luigi U to be more challenging than Mario U, especially while trying to collect every Star Coins. Beating a level and going after collectibles, all without a checkpoint, reminds me of older Mario games.
Other than that, you'll find Luigi U to be largely the same. New Super Luigi U follows the exact same story as Mario U, with the exact same bosses, exact same worlds, graphics, and music, and the exact same number of levels. The differences lie with who you play as, the much shorter levels, the addition of the invulnerable Nabbit (who helps you along should you die too often), and some throwback power-ups from New Super Mario Bros. Wii.
Even though I remain a huge Mario fan and will likely play his games until the day I die, I found it difficult to like New Super Luigi U. For any Luigi fan this is a must play, but as with New Super Mario Bros. U, I felt there were too many side-scrolling Mario titles released in too short a time without another gameplay change to break it up. So, I'm just going to say: If a Mario fanboy says it's too much, then it's probably too much.
Developer: Nintendo EAD
Release Date: June 20, 2013
Number of Players: 1-4 (Campaign)
Platforms: Wii U eShop (Reviewed)