I absolutely love the Doom games, it's a close contender for my favorite game series. I love to get more Doom whenever I can, and thanks to all the mods and addons constantly being created that's never a problem. The guys at id Software felt the same way, they wanted more Doom even as they were making it. This is why they were very open to the modding community, and very open to licensing their engine to other companies. Midway handled the console ports of Doom to the Sony PlayStation and the Sega Saturn. However, when it came to the Nintendo 64 they decided to not just port the game and go with something more original. Originally titled Absolution, they went with the much less cool name of Doom 64.
Going along with the previous console ports, Doom 64 hits most of the same notes as the original Doom but with various changes. All the weapons are there, the chainsaw, pistol, shotguns, chaingun and so on. The game features all the same enemies, with a few removed (like the arch-vile, which makes me glad). A couple were added including the nightmare imp and a new final boss, the Mother Demon. Much like the previous console ports the game forgoes the MIDI rock tunes for full-on ambiance and scary sounds. I honestly prefer the MIDI rock that some would call cheesy, but I can appreciate the scary tones as well. The game also features much better lighting effects, much like the Playstation Doom ports. It really adds to the atmosphere, but feels a little overdone in places. Overall the atmosphere is much more dark and brooding, and it really stands out for it. All this in mind, however, the game still runs off the good ol' Doom engine (also called id Tech 1). The story is just as throwaway as the previous ones, and involves the new Mother Demon final boss.
The most notable change between this game and the original its based on, is it looks completely different. Every single graphic in this game is different than the previous ones. All of the weapons and monsters get new pre-rendered CG art instead of the digitized and hand pixel art of the previous game. The textures have also been completely re-done. Being a long-time Doomer, I'm a little conflicted on this, honestly. On one hand, Doom 64's art is more consistent than the original, but it just doesn't have the same charm. Being so used to the older games, its strange to see all these familiar monsters with new looks, but for the most part you can still recognize what they are. They totally ruined the beloved Cacodemon, though. Another thing to be said is this game is pretty dark. I mean, okay, the original game was pretty dark too, but it hardly compares to the brightness-cranking required by Doom 64. 64, however, still does not compare to Doom 3. (Go see my review of Doom vs Doom 3 for more on that.)
Gameplay wise the game doesn't stray far from the original, but can be quite a bit different if only because its on a console instead of a PC. For one, the original game allowed you to save at any time, this one is a little more complicated in that regard. Saving only happens after you beat a level, and only if you have a memory card. The developers opted not to put SRAM into the cartridge, so you have to have a memory card to save, but there is also a password option available. (In fact, loading save games is still done through the "pasword" menu, confusingly.) However, a result of not being able to save at any point makes it more aggravating that the game doesn't give you back the weapons you had when you die, and have to start with a pistol. You could go back and load your game, sure, but it's tedious using the menu with the controller. The level design in general is much more puzzle-y than Doom proper, but that's not a bad thing. I really like the level design in 64 overall.