I recently moved to the US and I hate its coins. To the point that I consider all of them unusable. When I get home, I leave all the coins that I received as change on a plate by the door, hoping someday I will bring all of them at once somewhere to change for bills (I believe there are machines that do this).
My complaints:
i) They do not have numbers on them!! You have to read words to know the value
ii) To make point i) worse, they have nicknames printed on some of the coins!! They do not write "ten cents", it is "one dime". They do not write "twenty-five cents", they write "quarter dollar" (even the unit here changes)
iii) To make points i) and ii) worse, there is no default place where the value is written. $0.01 is a horizontal banner. $0.10 and $0.25 are round-based by the edge of the coin. $0.05 is round-based, but not by the edge of the coin, just slightly above another text that is by the edge.
iv) The coins do not obey a coherent progression of value and size. From smallest to largest the coins are: $0.10 < $0.01 < $0.05 < $0.25
v) The colors are all the same, except for the $0.01 coin.
So when you have a bunch of coins, you have to properly spread them in your hand to be able to compare their sizes (which is hard when the items are circles), account that there is no size-value correlation, and if you do not remember by size; you have to read a tiny sentence, lost in the middle of several other sentences, with no typographic differentiation of where they are.