There are a few key cards in gaming history, where important features were introduced. These are the most important ones IMO.By that same token, one could argue the GeForce 3 was more important because it introduced programmable shaders. GeForce 256 with its fixed function T&L would seem like a dinosaur in comparison.
Then one could argue that the Tesla line was more important than its predecessors because it was the first GPGPU and, not coincidentally, the first CUDA supported product. (I actually currently support this opinion, because we still consider modern GPUs GPGPUs.)
Then we got Tensor cores with introduction of Volta, which opened up AI as we know it today, Deep Learning, etc.
There are many "firsts" when it comes to the history of Nvidia.
- Voodoo - The first 3D accelerator on PC that would both improve image quality and framerate. Needed a second card for 2D rendering, all 3D rendering was fullscreen and the passthrough was not ideal though.
- GeForce 256 - Moved the image processing off the CPU instead of just accelerating some parts of it. Games ran so much faster than previous generations and you got much less CPU dependent. Back then a good CPU cost more than a good 3D accelerator.
- GeForce 3 - Programmable shaders opened up a lot of possibilities and removed almost all the performance penalty of 32bit colors. Was quickly made too slow though and 4 series was where you really managed to take advantage of the shaders. Still remember being blown away by Max Payne's effects and shiny surfaces.
- Ati Radeon 9800 - DX9 card which enabled lots of new effects and brought games significantly forward. Nvidia's first DX9 offerings were pretty bad and Ati dominated the performance in DX9.
- GeForce 8800 cards - DX10 support with lots of power. Crysis was just ridiculous in DX10 mode at the time, basically years ahead of anything else.
- RTX 2000 series - RT has the potential to take fidelity far beyond older lighting techniques. The 2000 series itself is generally too slow to run it natively and pretty much only the top cards in the 4000 series are 1440p cards with meaningful RT without DLSS. I do believe RT does have massive potential and makes a significant difference in the few titles that have implemented in a meaningful way. My guess is the true breakthrough of RT will be 6-18 months after the next gen consoles launch.