If you are looking to play NES games today, the "99999 in 1" ROM is generally considered a novelty item rather than a practical solution.

If you download the actual file called 99999 in 1.nes (single file, size ~3MB), you will open it in an emulator like Nestopia or FCEUX, see a flashy menu with a dragon, and discover that options 1 through 30 work, but option 31 crashes the emulator.

The appeal of the 99999-in-1 ROM isn't about finding high-quality, modern gameplay. It is about pure nostalgia, curiosity, and comedy.

(requires a modified controller setup on modern emulators) Contra (frequently hacked with the Konami code pre-applied) Galaxian or Galaga