i had some all night gaming sessions with Ninja gaiden 1-3. I think i spent about 7 hours straight playing the last level of Ninja Gaiden 1 before i beat it. I think i beat 2 a little bit easier. 3 i gave up after several tries because i had to keep starting over because of limited continues.
I beat ninja turtles on NES as a kid, though it's damn hard.
Ghouls and ghosts i beat after playing it for like 5 days straight.
Battletoads i spent a couple nights playing the entire night, and i couldn't beat it.
Castlevania 1 i beat after many many days of constant trying, i admit i beat it much later on the wii so i didn't have to leave my NES on forever. It's hard to say, but between the medusa heads and knights, doom, and final boss i spent a couple dozen hours i think.
Castlevania 2 is not hard, I dont' really understand this. Yes it's cryptic, but the gameplay is not that hard. The bosses are a joke, they are easy as hell.
Castlevania 3 is really hard, i admit i never beat it. I didn't try as many times as the first one.
Castlevania 1 may be the hardest, the thing is I think i played that same part over many hundreds of times.
currently playing: Skyward Sword, Mario Sunshine, Xenoblade Chronicles X