Doom 64 is pretty rad... it's the only reason I'd consider buying another N64.
Doom 64 is THE reason my N64 stays hooked up. I love my N64, but I'll be the first to tell you some of those games have aged poorly. I poured more hours than I could count into Goldeneye back in the day, but today, it's barely playable to me. I recently tried to pick up Quake 2 again on that system since I also played the hell out of it back in the day, can't do it. The controls are... bad. N64 staple Ocarina of time? Again, same deal, but the 3DS version made the original impossible to go back to, it just looks hideous by comparison.
There are still games that are still a lot of fun for me to go back and play, like Doom 64, Mario Kart 64, Blast Corps, F-Zero X, Ogre Battle 64, Paper Mario, Turok 1 and 2, and somehow, both Castlevania games (I got nothing for you there, I know they look terrible, and handle pretty funky) and more I can't think of off the top of my head. But a lot of games on that system either have vastly superior remakes, or have just not aged well at all.