While it still did give us some great stuff, such as Pokemon Red/Blue, Tetris, and of course, Link's Awakening, and it birthed Kirby, Pokemon, and Wario, on the whole, it's a really rough system to return to that was bettered by almost every single one that followed.
Gameboy was out on the market for a decade, which included a fair few years where Nintendo just sort of ignored it, and a lot of the games on it were fairly simplistic with little depth that are hard to go back to today.
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Their supremacy in the handheld market has been uncontested and unbroken - challengers from Atari, Sega, Nokia, Sony, and so many more, have all tried and failed to unseat Nintendo in the handheld market. One could argue that Nintendo's true legacy in the market is in the handheld arena - their very first hit ever was Game and Watch, a portable gaming machine. And for almost that entire time, Nintendo has been making handhelds too. Nintendo has the longest continuous history in the video game market, with home console hardware going back to 1977 - meaning they've been doing this for almost 45 years at this point.