Wii Motion Plus isn't a videogame. It's an add-on enhancement to improve the motion capabilities of a stock Wii remote (And is factory integrated into later Wiimotes) in the handful of games that support that functionality. And most of those that can take advantage of it require Motion Plus.
Or are you talking about the difference between Wii Play and Wii Play: Motion? They're two separate minigame collections with different game lineups in reach (Although a couple in Motion are updates of minigames from the original). Both rely largely on motion control and feature the Wii's signature 'Mii' characters. And in the case of Wii Play: Motion, it requires a Wiimote with Motion Plus to be used. And I don't recall any locked games.
They're both just so-so which is hardly unsurprising due to almost being freebies with the purchase of a Wii remote. Even with multiplayer which is their forte, it's unlikely that they would have much in the way of replayability for the average person. A round in each minigame was enough to satisfy me besides the tank minigame in the original Wii Play which saw me return to it several times.
I rather liked that one. It reminded me of the tank minigame in the arcade game Tron from 25 years ago, Atari's B&W arcade tank games from the 1970's, and Combat on the Atari 2600 and several other console contemporaries from other companies.
I'd buy an entire game based off that if more features were tossed in to add variety and a bit more depth and strategy.
Would make for a nice e-Shop release.