Maybe it's just me but I don't remember getting as frustrated with the other hitman games (I've played them all.) I remember hitman 2 being the hardest, from the old games, but absolution just frustrated me the most as far as I can remember. I think the old games allowed you so many saves in the middle of a mission though.
I don't know if getting older has made my patience deteriorate, or maybe the fact that I'm so busy all the time makes it harder to enjoy games like I used to... or maybe trophy/achievement hunting...
Either way, it was very satisfying to beat the game on Hard, and get the achievement for 100 challenges as the credits rolled (i had exactly 100 challenges done by end, so coincidental :P). I probably made it harder for myself by trying to do infiltrator on almost every mission on hard. But that's the way hitman is supposed to be. The lack of mid-mission saving or checkpoints really made it suck though imo.
But which hitman game is known to be the hardest? --- Playing: ME3, DR2, Waiting for: GTA 5, FFvs13 --->> http://us.playstation.com/playstation/psn/visit/profiles/Magus1724