Castlevania II: Belmont's Revenge

Across-the-board improvement to C:TA. Better presentation (with smaller sprites, allowing for bigger areas, better animation, and tighter controls. The linear level structure has also been replaced with a stage select screen, giving the player choice and visual diversity - and some of these places are bad ass, like a crystalline castle or grifty dungeons. The platforming sections are refined, too, with far less impossible jumps and a more forgiving coyote time window. And do I even need to talk about the soundtrack? It's sick and there's even more tunes here thanks to multiple songs in single stages.

Still completely unforgiving, and it's still slow as sin, but this is a massive improvement over the original and is definitely recommended for Castlevania fans.