I'll give you two since I haven't played enough for a full 10, looks like I'll have to try some of the top recommendations here.
Castlevania 3: Dracula's Curse
The game I love to hate, I'd like to say that CV3 is tough yet fair but that would be ignoring the high levels of dickery the game can unleash upon the player. Still the level design mostly leans towards a tricky yet manageable setup that has to be tackled in an almost precise methodical manner, you don't try to rush through CV3, that's the moment you lose. It's all about keeping your head no matter how many times that respawning bat is going to pop in from the left or right of the screen while you chip away at the durable axe knight, it's about studying the lay of the land and taking note of how the position of a staircase can affect your ability to crouch and throw subweapons due to the games rather unfortunate control limitations. At some point after numerous continues it all clicks and you finally have the right path through the stage figured out as you storm through with precise and near predictive whipcracking, picking the right sub weapon for the situation and showing those damn pesky crows (Dracula's most deadly underlings) that you're not afraid of them anymore. Then the next stage begins and the process begins anew.
Level design is a spiffy step up from the original game, now with more platforming gimmickry than before complete with that fixed jump arc that gives the game's platforming something of a sadistic charm. Yep it's not just the combat that requires a bit of thought before progressing, every forward or backwards leap taken cannot be altered, one must commit fully to their jump decision, commitment is in fact something of the core to both sides of CV3's action platforming and what defines it.
Stages don't just take place in the castle which widens the scope a bit, flooded ruins, monster filled marshes and a ghostly ship are fitting escapades for a game with this cheesy classic horror theme.
Diverging paths through the world map give you choice in how to reach Drac's abode, difficulty wise that choice is kind of like choosing between getting punched in the nuts or kicked in them instead, either way it's going to hurt but hey choice is always appreciated, well until it turns out you walked down the one path that leads to the section of a stage where it builds itself up brick by brick, well I didn't say this game was perfect.
Speaking of choices you can get one (and only one) partner to tag along with Trevor through his journey which can greatly alter the options you have in approaching stages, Grant's crazy clambering and superior jumping can give you an easier time platforming while Sypha's tomes of magic make for some incredibly formidable attacks (those magic orbs man), in any case they're a greatly appreciated addition.
CV3 is an odd game in that while I enjoy it I feel as if I need to mentally prepare for even playing it, each stage is like a mini endurance run, the sum of which all together makes the journey to the castles keep and eventual elimination of Dracula feel like a long hard fought journey that while satisfactory also brings a sigh of relief that at last it's finally over and I'll never have to see that one bat hanging around the end game pendulums again.
Then for some masochistic reason I'll play it again and rage a little more.
Mega Man 3
The main additions for Mega Man 3 almost sound like last second scrambling for sequel justification, the ability to slide briefly across the floor and painting over the MM2 items with a robot dog skin are far from game changers but refinement is the name of the game and it turns out that sliding is in fact rather fun and robot dogs give even a spring function personality.
MM3 begins the greater trend of guess work when it comes to figuring out boss weaknesses with the design concepts getting further out there, I'm not sure what the logic is for say homing snakes being the slayer of evil robo twins and things get worse when the MM2 crew return for a mid game difficulty spike where I never remember the weaknesses but those mid game blues aside MM3 just about manages to edge out 2 and 4 to be my favourite of the NES entries.
Level design feels more coherent and well structured than Mega Man's second outing, it still has some sore spots like the repetitive Gemini Man stage but all is forgiven when going through Top Man's wierdo greenhouse stage with giant cat robots and spinning top platforms. In any case MM3 has a nice blend of interesting platforming concepts and distinct enemy types, each Robot Master stage is memorable for its own reasons and it's not even that bad when four of them return for a tougher second round later on though oddly the following Wily Stages are noticeably easier so the game's difficulty is a bit all over the place. Character control is as finely tuned as ever giving you a great degree of character control which is par for the course for the series and you'll need that deft touch to make those leaps that'll have Mega Man attached to the edge of a platform by his single pixelated toe.
Between character additions like Rush and Protoman, the strong stage music and distinct stages MM3 feels like the game that really imbued the series with the most personality, while following games would add more characters and tweaks to the gameplay formula it all starts to feel rather rote, MM3 in a way is like the peak before the decline as far as the NES games go and while the two on either side of it come close MM3 has that edge that makes it my favourite of the fast paced yet precise action platformers.
Random question time, what's the consensus on Ninja Gaiden 2? I enjoyed the first game up to the endgame point of ridiculously punishing stages that I just can't manage, I'm kind of intrigued to try the sequel but also cautious.