Bunch of things really. The game's controls and A.I. have not aged gracefully, but it still houses ideas that oddly don't seemed copied enough.

I still like the one big un-healable health bar for one. Halo's recharge nonsense has created a generation of shooters where you constantly hide behind corners, pop out, get hurt, hide, etc etc. Honestly, all though it's nice to not scurry for health kits, it sucks the sense of excitement out of the game. In GoldenEye you only had a few pieces of Body Armor per stage (if any at all) and no way to bring your health back up. As your health goes down, it really creates a sense danger knowing you can't bring it back up, and armor is usually very limited. You feel challenged to really pull it together, not challenged to stay in cover for ten seconds, or run back to health kit you saw a little earlier in the stage.

The big non-linear levels coupled with multiple varying objectives are still very much a favorite of mine. You certainly feel more spy like feeling around different rooms, looking for your next objective. Especially when your objective is something that may not be obvious, like attach a covert modem to enemy surveillance equipment. When most shooters break from the action, they typically throw something obvious in your face, like a puzzle, and everything dangerous is turned off long enough for you to finish. In GoldenEye these kinds of things are hidden around the stage amongst the danger, and you get more of them as your turn up the difficulty no less. You can't just shoot your way through everything because you might kill hostages or blow up computers you need and blow the mission.

Well for me what made it great was the multiplayer. I have great memories of playing it with 4 friends for hours and hours on end. I can't really say exactly what made the multiplayer great though. I'm not really much of a critic. Still, who would have thought that a game based on a movie could possibly even be this great.

Multiplayer. It was the first 4 player at the time i think. I could be wrong. Gameplay was great. And it could be played however you wanted to.... Guns blazing or stealth.
Goldeneye/perfect dark remains my favorite shooters to this day. No other shooter got as much attention from me as these games did. Not even close.

and so how come the other 007 games never got the magic back?

Well.... rare is not what they used to be in the N64 era.... maybe??? is rare still in charge of the 007 games?

The success comes from the license itself, the quality of the game (controls, gameplay), multiplayer (It's so funny with the golden gun rules) , and replay value with the tme reward in each level. The next bond games missed those elements (except the license) and when compared to goldeneye, suffers from that.

I think Goldeneye really led to the taking off of the multiplayer market along with the shooting market on consoles. Just never seemed to be there until after that game.

As a real Bond fan, part of the experience was knowing that each of the maps were constructed to accurately reflect the environment shown in the movie. Really made ya feel like Bond.

I loved it because it was the first FPS I played that didn't involve mindless shootings, you had specific and fun missions to do besides shooting enemies...

Wow, how does that remind me of a certain series from the big N that just released a few days ago...! :/