I could probably provide you with pages of issues but they all bundle into a couple of major categories

1 - unbelievably poor context presentation, e.g. if I paste? where in the file system will something end up? Who knows? Where am I in the filesystem? I can guess! Is it correct? not usually. How about let's play the game of which kind of file is this? Because filenames usually end up with a '...' somewhere in them and I have to fiddle with Finder every single time to get it wide enough to stop truncating filenames so I can figure out which file is "P1250416.JPG" vs "P1250417.JPG". Folders mix in with filenames when sorted so navigating up and down the tree takes forever (and is harder to do keyboarding). And on and on and on.

2 - completely nonstandard keyboarding and navigation, e.g. ENTER to rename, cmd+o or cmd+down to open a file? really? In which way are either of those possible intuitive? It appears Finder is trying to follow some impossibly ancient keyboard shortcut system that was probably put in place 30 years ago and doesn't make any sense at all.

Here's a typical use-case for me. I just shot about 3,000 photos and I want to do a quick pass on the photos and delete bad photos and move photos of a certain kind (photos with a certain subject) into another folder. In explorer it's a matter of hitting "enter" then "right" until I see one I don't like then hitting "delete" to remove it then continuing with "right" until I find more to delete or finish the bunch. Moving ones with a specific subject involves me ctrl+mouswheel until the thumbnails are as big as possible so I can see the subjects, then ctrl+lmb on all the ones I want to move then ctrl+x, move into the folder, ctrl+v (and now they're all sorted and not scattered all over the place like in Finder and I moved them using the completely system consistent cut-paste keyboard hotkeys) and alt+left to go back (just like a browser). Other niceties like being able to maximize and then restore back to the default window size with a couple mouseclicks are also smoother.

In Finder all of this becomes work instead of a few minutes of repetitive keypushing. I can almost do the entire workflow without a mouse in Explorer, and where I have to mouse it kind of makes sense (picking specific items from a group) over a keyboard. But in Finder, just to get started, I have to buy and install a couple pieces of software.

Sure most of these things can be "fixed". If I install this or that extension, and customize finder in this or that way and remap such and such keyboard hotkey I can kind of end up with a sane workflow and filenames I can actually see. But I shouldn't have to fix shipping software. Everytime I open Finder I'm asking myself if anybody at Apple actually uses it.

Take a look on the internet for people complaining about Finder and most of the complaints are more or less along the same lines. The complaints are consistent and have been going on for years. Solutions have been hacks since forever as well and usually involve installing $100 of replacements, addons or fixes.

What's amazing to me is that these problems don't exist in any other GUI file manager I've ever used, from the Amiga to my TI calculators. Finder is just rubbish.