Yes, they are very different.
The sound of MX on videos is often the same due to the video maker bottoming out really hard all the time. Many MX sound clip videos I have seen are like this.
Blues and Greens are clicky and the switch itself makes a sound, Reds, Blacks, Browns and Clears do not make a sound, but on all the switches, when the switch slider hits the bottom of the casing it makes a "clack" and again if you release the slider quickly it makes a sound when it hits the top of the casing.
The three main types definitely feel different from each other (clicky, linear, tactile), although the clicky and tactile can feel similar. Greens are the same as Blues, but with harder springs, likewise Blacks and Reds. Clears are very different from Browns, though, and have a much bigger tactile bump and springs with a different spring constant / force curve. They start off light, but get harder quicker. Browns are tactile enough to prevent typos and accidental presses.
Also, as others have mentioned, there are other factors that affect how a keyboard feels such as case design and material, plate or PCB mount, keycap profile and mass, etc.
The "sound dampeners" you mention are actually small orings that you place on the keycap stems. They cushion the bottom out a little, dampen the sound and depending on how thick they are they can reduce the travel a bit. I like them on tactile (Brown and Clear) switches, but I much prefer adding little silicone balls inside the switch to do the same job (trampoline mod), since those are not dependent on the keycap design and don't change feeling when swapping keycaps.
So should I buy reds,browns,maybe blues again?
Depends what you want... If you want to be able to "hover" around the actuation point for FPS games, then get linears (Reds or Blacks). If you need tactile feedback when typing, don't get linears, but rather clicky or tactile. If you like the sound of the clicky switches and it doesn't matter if your board is noisy and you don't mind the hysteresis (actuation and reset point in different positions), then get clicky switches (Blues or Greens). If you want a quieter board, but still want to feel when the switch actuates, get tactile switches (Browns or Clears). If you want light tactile switches with mild tactility, get Browns, if you want more pronounced tactility get Clears. My personal favourite is Clears, specifically modified with trampolines, stickers, 62g springs, lubed, plate mounted, aluminum case and SA profile keycaps
