If you have AA or AF forced, some effects won't work. Sometimes it makes it look bad, but other times just not as good. ENB also looks best when using its own transparency AA, though depending on other settings, that may make it run fairly slow (it's a highly variable thing, usually being a minor slowdown, but not on all presets, probably due to how it may interact with other effects used). The lighting changes using ENBs make quite a difference, but the rest, even if it looks great while not playing, often seems to disappear when immersed in the game, IME. I can get a couple ENB presets looking like screenshots and videos, right now, just not the ones I want to use (I don't want an over-vibrant, "cinematic," look, but Vividian Vanilla and Phinix Natural, which worked fine with a prior install, don't want to behave this time). Damn y'all for making me go at it anew (OK, I really have been meaning to, but needed motivation)!
If it is looking a bit dull, try changing in-game and in-ENB brightness and gamma. +0.1 gamma can make a world of difference.
Also, they usually have their INIs tweaked for color, foliage density, etc., along with vibrant environment mods (Vurt makes TESes look better, period).
2K/4K textures make a difference most for up close objects, like sacks, barrels, tree bark, some weapons, NPC clothing, and plants. It's nice to have all 2K or better, but while the difference is huge for a cloak, or berries, it's barely noticed as an animal's skin texture, or the ground texture (and, it's a waste, IMO, to get half-sized normals, since normals and parallax are what make more detailed textures look better, as much as the [A]RGB pixels for objects, and more-so for the environment), yet can chew up VRAM just the same. With clutter, the main advantage in both better textures and meshes is not needing to look as hard, with smoother curves on bottles and plates, and textures that more clearly look like what they are supposed to be, instead of, say, oval pink fuzz being meat.
Finally, the Youtube videos showing them off always skip over parts of the game not properly fixed, with low-res content not yet replaced, etc..