It was really slow going the first time, but as somebody who really isn't into horror, I was pretty surprised at how many I recognized.
I assumed it would randomize the order every time because I noticed that there were some characters who weren't used the first playthrough, but then when I read that the image was made by somebody else, I understood that characters weren't added specifically with the intent of including them in a game.
I would have preferred to have the game enclosed within a border, since the screen autoscrolls with the cursor, and some of the targets are very close to the edge, and also the existing HUD elements cover up some of the characters (although none of the actual required targets seem to be covered up by them). An external border would allow for the various buttons and target list to be displayed, as well as time, score, found, fails, etc. without having to open the menu to check relatively trivial stats.
The menu wasn't explained very well in advance, so I didn't bother to look at it on my first playthrough. That being the case, I didn't know about the "skip to [x]" option until after I beat the game. Maybe add a splash screen after starting a new game, with a quick rundown of the contents.
Because the "win" screen doesn't close, when I actually DID open the menu after my first win, everything was covered up and there was no way for me to see what was on it. Maybe add the ability to close the win screen, or add buttons on it to specify your successful graves or to take you back to the main menu.
I really dislike the fact that when you unlock a new level, it skips ahead a bunch and you have to manually back up to get those targets. Even if I knew about the "skip to [x]" option, it wouldn't necessarily get me close enough to not have to click the arrows a bunch of times to get to a valid target.
I DID like how if you found a target and the next target was already checked off, it skipped you ahead to the next still-needed target. I wish it did that after #100 and looped around so I didn't have to do it manually as described above.
I had some issues with graves/medals in that I only had 3 left to collect today but in-game it said i still needed 5. I couldn't tell which other 2 I wasn't getting credit for because all the graves are identical and have no text explanations. Even without adding text to them, maybe you could add little horror-themed icons on each grave so that we can identify them in-game.
I had a hard time getting the "Cheat" medal. I tried all kinds of tab-tricks and right-clicking, but nothing paid off, so I ended up checking the walkthrough to see if it explained how to get the medal.