Personal favorites, other than Castlevania, I'd love:
A REAL Double Dragon attempt that is NOT like IV. If they can get the NES+ style down (not like IV, which they sucked at), I'd be fine. If they can't, go for a sorta Arcade/SNES+ looking version with all the leveling and moves of the NES original.
Splatterhouse. Basically a Splatterhouse IV that is a cross between Arcade and Genesis+ graphically.
EDIT: Of fuck, I remember I always had a dream of a TMNT BEU with graphics that look to par circa the first arcade game and Turtles in Time. My idea was to have a big final battle against Shredder, the Foot, Krang and such, in which, which takes the Turtles from the streets, sewers and Central Park of NYC to Dimension X itself. Will feature cameos from other characters, such as the Punk Frogs, Ray Fillet, Mona Lisa, the Neutrinos and others. Basically, a love letter to the classic TMNT BEUs of the early 90s and a big love letter to the 80s TMNT cartoon series, all wrapped up in one pizza poundin' adventure.
Yes! Something that feels like a classic FF game, big world, lots of towns, adventure, whimsy, more than one "world", but unlike Final Fantasy Legends/Dimensions, tone down the nods to other FF games. It is alright if an item, boss or summon nod to something in past installments, but we don't need fuckin' locations from past FFs appearing in the game. That and no more
as final bosses. Make the final bosses original, dammit!
Ninja Gaiden is the real standout to me. One of the best 2D games of all time and no proper sequel since the 3rd.
I would say Contra as well but Contra 4 on the DS was satisfying. I also wouldn't mind a faithful sequel to Super Castlevania IV.
Ninja Gaiden and Contra are wonderful choices.
I could go with just the SEGA ones
Streets of Rage, Golden Axe, Alex Kidd and Shinobi
All those are GREAT choices. Hell, as people are listing RPGs, I'd love a classic styled Phantasy Star V (done in a sorta Genesis+ style, taking inspiration from Phantasy Star IV's style, but goin' up from there).