Somewhat surprisingly, Diabolik is an adventure game with the basic control structure of Grim Fandango, interspersed with little QTE-like mini-games for actions like knocking out a guard stealthily or fighting someone. Unfortunately, it's also one of those adventure games where 50 obvious and reasonable solutions to the puzzle at hand don't work because LOL, and the one that does is some ass-around-your-elbow moon logic bullshit. This leads to much of the game being the joyful experience of listening to Diabolik be a Can't Cunt and mumble "NO! THAT MAKES NO SENSE! I CAN'T DO THAT!" as you suggest perfectly reasonable courses of action.
Outside of Italy, Diabolik is mostly known as the target of ridicule for MST3K's final episode
. In Italy, however, he's kind of their equivalent of Golgo 13; a long-running comic and graphic novel star who is an amoral sociopathic dickbag who steals shit from rich people instead of an amoral sociopathic dickbag assassin. Our story here is just a little slice-of-life adventure for him full of "THEN WHO WAS PHONE" as we open with him apparently killed, then his partner Eva apparently gets killed, but of course neither one of them was actually phone.
Anyway. The game really isn't hard, as it's extremely (one could say "stiflingly") linear, and relies on flashing hotspots to show all interactive points while also usually only limiting you to a handful of small screens at a time. Of course, games with this simplistic structure usually generate challenge by doing something obnoxious, and Diabolik is no exception. The game is best summed up by a sequence of events in the opening chapter that will very quickly give you a good indication of whether this is something you really want to play or not. Early on you're trapped on a screen where you're underneath a train you need to get on board. The only point of entry is a window above you, guarded by a dude leaning out it having a smoke. The only interactive points on the screen are the guard, the window, and a railing between you and it that you presumably need to clamber on to reach the window (given the perspective of the camera angle.) You knock the guard out with a convenient sleeping gas mine you just happen to be carrying about, and then you have an unguarded window in front of you. The sensible thing at this point seems to be to climb or grapple the railing to climb up, but neither works. OK ... grapple the window directly? Nope. The answer turns out to be to "LOOK" at the out-of-reach window, which then sets off an automated cut-scene of Diaballick scrambling up to it. But wait, there's more! Once inside, you have the unconcious carcass of the guard in front of you. LOOKing at him tells you "His clothes could be useful!", but then when you actually click USE on him? "It's a waste of time!" The solution ends up being to go into your inventory and use a mask that you've been carrying around on the guard. This also, for some reason, has to be done directly from the inventory, when that's not needed to ever use any other item to this point. Jesus H. Christ, game. I describe this all in loving detail because it's not an isolated incident; this is how 90% of the rest of the game works too. This is what you have to deal with the whole damn time you're playing.
The game's cutscenes use that ugly, stiff Flash art - it looks almost exactly like that game Shank - but it actually has a surprisingly decent soundtrack somewhat reminiscent of the ol' Goldeneye and Perfect Dark soundtracks. Maybe it's a nod to the shitty film, which was terrible all around but somehow managed to get Ennio Morricone to compose the score? Probably not, but I'll pretend that it is.
Appropriately, the last two lines out of Diacocklick before I gave up on the game were "Why should I?" and "I don't have time for this!" (whilst knowing the next step in a puzzle but trying to figure out what finicky-ass place the game wanted me to actually use the item at.) Sums up the game in a nutshell, really.