I'm posting this here because YouTube comments only have 500 characters.

Ok. Here we go:
Firstly, you are wrong about opacity: Both water and the breaking animation support partial transparency.
Now on to the textures:
I know this is 4x, but that is no excuse to have solid-colour blocks. Those look hideous (imo) and if you are going to do that, keep it to it's own themed pack where all the blocks are like that, and then delete it because we already have millions of those.
So please change Grass, Dirt, Stone, Side-Grass, Wood, Sand, Mycelium, Side Mycelium, Noteblocks, Juke Boxes, Clay, Snow-Side Grass, Snow, and Stone Slabs.
Just because it's 4x doesn't mean you can't put different shades of colours in there, so it isn't monotone colour.
Saplings could use some more branching out, rather than just a 2x3 lump, and why do the birch and pine saplings have partially transparent colours on them?
If you want Bedrock to look distinct, I recommend making it out of darker colours. Dark grays and blacks will make it near-impossible to confuse with cobblestone.
IMO Glass should have a border around it, instead of that random dot. If a glass texture has no edges, it just looks plain strange in-game.
I recommend doing what you did with stone bricks to the normal bricks, because currently the bricks are just a grid of two different colours.
What's up with the completely invisible pixel on the ice?
Torches, Levers, and RedStone Torches look horrible when in a 2x3 slab, try something creative, like just using the flame particle as the 'torch' and then use the actual texture as a holder for the torch or something.
Why are there partially transparent pixels on the wheat, and minecart rails?
Why is the side of the glass-pane only one pixel? You'll need more than one to cover the entire side.
The 'On' RedStone Repeater should be a brighter red.
The sides of the bed are too low.
Around the Giant Mushroom/Cake section, it looks like someone put a large brown scribble over several textures.
Partially transparent pixels on the unused cake icon, as well.
Why is the second redstone texture made entirely of partially transparent pixels?
Nether Brick could also benefit from using the same style texture as the Stone Brick.
Your GUI elements still use the resolution of a 16x pack, you'll want those to be 64x64.
Armor is also using the 16x resolution. A proper 4x pack would have them at 16x8.