It's no secret that Nintendo's (NTDOY -0.57%) Wii U is falling behind Sony's (SONY -0.46%) PS4 and Microsoft's (MSFT 0.09%) Xbox One in the next-gen home console race. The Wii U has sold 6.2 million units worldwide, putting it between Microsoft's 4.5 million Xbox Ones (5 million sold-in) and Sony's 7.7 PS4s, but it launched a full year before both consoles. However, I think investors and gamers shouldn't overlook the strong sales potential of two key titles for the console -- Mario Kart 8 and Super Smash Bros. for Wii U. Both titles could provide a much-needed mushroom boost for the Wii U, which only sold 310,000 units last quarter.

Mario Kart 8 and Super Smash Bros. for Wii U. Source: Nintendo.

Two of Nintendo's most enduring franchises
Mario Kart 8, which will be released in North America and Europe on May 30, is the latest installment of the 22-year-old racing franchise. The series, which debuted on the Super NES, has sold over 100 million copies to date. The previous home console title in the series, Mario Kart Wii (2008), sold a whopping 34.4 million units and helped Nintendo eventually sell 101 million Wiis worldwide.

Super Smash Bros. debuted 15 years ago. The first three titles -- which were released on the N64, GameCube, and Wii -- have together sold 24.8 million units. The Wii version, Super Smash Bros. Brawl, was the top seller of the series with sales of 12.1 million units. This summer, Nintendo will release Super Smash Bros. for 3DS, followed by Super Smash Bros. for Wii U by the end of the year. The two versions will be cross-compatible with one another.

Super Mario Kart (1992) and Super Smash Bros. (1999). Source: Nintendo.

To understand how huge Mario Kart and Super Smash Bros. could be for Nintendo, consider these numbers.

The best-selling title so far on the Wii U has been New Super Mario Bros. U, which has sold 3.97 million copies. By comparison, the best-selling titles for the PS4 and Xbox One are Activision Blizzard's (ATVI) Call of Duty: Ghosts and Electronic Arts' (EA -0.47%) Titanfall, respectively. The PS4 version of Call of Duty: Ghosts has sold 2.23 million copies, while the Xbox One version of Titanfall has sold 1.78 million copies.

If sales of either Mario Kart 8 or Super Smash Bros. for the Wii U can hit 5 million to 10 million, it would be a huge accomplishment for Nintendo. Nintendo's strategy of bundling those exclusive games with its consoles could move a lot of Wii Us off the shelves.

Can Nintendo move forward while constantly remaking old games?
Although Mario Kart 8 and Super Smash Bros. represent excellent opportunities to get Wii U sales back on track, the two titles also define Nintendo's habit of remaking its past hits repeatedly rather than developing new IPs.

When Super Mario Kart was released in 1992, it was a highly original idea that gave birth to the whole kart racing genre. In 1999, the original Super Smash Bros. tossed Nintendo's flagship characters into a chaotic combat arena with easy-to-learn controls. Super Smash Bros.' gameplay has since been copied by titles such as DreamMix TV World Fighters, Viewtiful Joe: Red Hot Rumble, and PlayStation Battle Royale.

Both titles were considered revolutionary. Mario Kart simplified racing games, which were often considered difficult to play due to unforgiving controls. Super Smash Bros. simplified fighting games, which had fallen into the habit of imitating the more complex controls of Capcom's Street Fighter franchise. This was Nintendo at its best -- the same brilliant company that reinvented the platformer with Super Mario Bros. and the adventure game with The Legend of Zelda.

Nintendo at its best: Super Mario Bros. and The Legend of Zelda. Source: Nintendo.

Unfortunately, that's a side of the company we haven't seen for awhile. Rather than take risks on launching new genres, Nintendo is content to remake old games with incremental improvements.

That's not to say that these games can't still be great -- Mario Kart 8 currently holds an impressive 89% rating at review aggregator site Metacritic -- but it's disappointing to see Nintendo not trying harder to remind gamers how great it can be.

The game's not over yet for Nintendo
In conclusion, if Mario Kart 8 and Super Smash Bros. sales come in strong, the Wii U could still have a fighting chance.

This could set it up for a strong comeback when other eagerly anticipated exclusive titles -- like Hyrule Warriors, Bayonetta 2, and the elusive Legend of Zelda Wii U -- finally arrive. However, if sales of Mario Kart 8 and Super Smash Bros. come up short, Nintendo might have to finally develop new IPs instead of relying on its older ones -- and that might not be a bad thing at all.