Don't see why they couldn't get N64 games to run smoothly since according to some reports, the iPad Air 2 is as powerful as the XBox, which was at least twice as powerful as the N64.
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There are way too many freemium games but that said, there are also quality premium games where you pay up front and never again. Implosion: Never Lose Hope is one recent example. Lost Within, from Amazon of all companies, is another.
The N64 was a very odd console to develop for in comparison to the PS1 and later Nintendo consoles. And it shows in emulation and ports of N64 games. It also does not help that the N64 was more or less a console for first party and Rare games because when I was doing a lot of emulation those were the only games to be even close to being playable and most people developing emulators aren't going to waste time on creating fixes for random N64 games very few people will play.
Even official ports and emulation by Nintendo aren't perfect when it comes to the N64.