When you look to a HD remake of a N64 game you're afraid to find an ugly game, and that's what happened: few polygons, cubic characters and objects, blurry textures, ...
But in the case of Perfect Dark, if you take a look to the N64 game in an emulator you will find an ugliest game, and that a big effort has been made to make the game far less ugly that the original version. GXL Redge has compared in the GXL boards the XBLA screenshots of Perfect Dark to the N64 Perfect Dark HD output of an emulator. The difference is obvious.
It's the same feeling of playing an old good game without the feeling of playing an repelling game :)