It saddens me when someone says the 3D Castlevania games before Lords of Shadow are inferior to their 2D counterpart, and find the LoS entries to be the best 3D CVs made. Worst of all, people don't give the N64 titles a chance. Castlevania 64 and Legacy of Darkness are put aside as titles some people want to forget exist. I love the N64 entries, and to me they're the greatest Castlevania games ever made. I find Lords of Shadow to be a step backwards compared to Legacy of Darkness. The levels are great, having four playable characters, upgradeable sub-weapons, vampires to fight other than Dracula who are normal enemies rather than just bosses and who can infect you with vampirism, the locations, day and night cycle, the soundtrack, and more! It's also more Castlevania than LoS in my opinion.
CV64 is different from LoD, the later being an upgraded version of the original. In Castlevania 64 there's only two playable characters, non-upgradeable sub-weapons, smaller enemy roster than LoD but still enough, and a non-controllable camera. That shouldn't mean the game is bad. It's terrific, and feels different than LoD. It also has different level layouts. When I first read a post from someone that said Legacy of Darkness was missing a few things from the original version, I was worried. However, that doesn't seem to be the case so far, with the Forest of Silence still having elements of the original but with a different level layout, the Castle Keep still having the same layout but with the doors being different and also sort of different enemy placements (maybe the doors and enemy changes are only for Cornell), and the mansion having new puzzles (maybe for Cornell only?) but is intact along with the garden maze. Maybe the user said that for Reinhardt and Carrie's scenarios? Once I unlock the characters, I'll see if they have been edited or not.
Thing is, you should get both games if you can and see the changes made to the gameplay and levels. To me, they feel different, but have the same story. Legacy of Darkness is non-canon to the Iga timeline, so the game is its own universe. I find that nice. :D