The NES had a clearly recognizable graphical style thanks to its distinctive color palette and technical limitations. But many developers seeking to evoke nostalgia for that era just don't get it, thinking that heavily-pixelated artwork is the same as making something "8-bit."
Thankfully, the developers of Odallus: The Dark Calling have no such problem; as you'll see from the screenshot below, the team's upcoming game looks very much like a genuine NES title. That's because they've used the NES' original color palette in all game graphics as well as most of the game's artwork and communication. Not only that, but they've respected the NES' inherent limitations on color and size of each image and sprite, which means no anachronistic graphical elements like parallax scrolling or sprites with far too many colors on them.
"But what is Odallus?" I hear you ask. A good question!
In the developers' words, Odallus is a "NES-inspired action exploration game" in which the curiously named warrior Haggis must infiltrate the demonic hordes and take down the Dark Lord. The structure will be classic old-school Castlevania at heart -- you progress through a linear series of stages rather than exploring a vast "open world" castle as in Metroidvanias -- but within each stage, there will be multiple routes through which you can progress.
Odallus is the work of small Brazilian indie developer JoyMasher, who last gave us the "NES hard" action game Oniken, itself a loving homage to 8-bit classics like Contra. The team at JoyMasher is keen to stress that Odallus isn't going to be quite as frantic as Oniken, since there will be a greater focus on exploration, but even NES veterans can likely still expect to be challenged significantly.
JoyMasher recently launched an Indiegogo campaign to fund development of Odallus, but notes that regardless of whether or not it reaches its $5,000 goal, the game will get made. The campaign is primarily intended to help the developers get paid while they are actually working on the game rather than afterwards, but a few stretch goals are in place for if the team successfully exceeds its target. It's doing well so far -- at the time of writing, funding is at $2,105 with 48 days left to run, so it's looking almost definite that the target will be at least met if not exceeded by a considerable margin.
You can find out more about the project on the official Indiegogo page. There's a free demo available, but JoyMasher notes that this isn't an extract from the finished game -- instead it's a "best of" compilation intended to show you all the different things you might encounter in the final product.