I expect you'll have a tougher time there because NES games were written directly in assembler, so there won't be the characteristic patterns that a decompiler

I expect you'll have a tougher time there because NES games were written directly in assembler, so there won't be the characteristic patterns that a decompiler can use to recognize particular control flows— I believe C wasn't really standard until the N64 era, which was part of what made high-level emulation (see: UltraHLE) possible. On the other hand, hand-authored assembly is easier to read directly, because, of course, it was written and read in that form originally anyway!