Bethesda's Morrowind is a tad long in tooth, having been released back in 2002, however, it's still considered the strongest game of the series, even if Skyrim gave a competitive showing. So loved was the game that modders are trying to recreate the former into the latter and yet another is attempting to rewrite Morrowind from scratch to include cross-platform support, better performance and maybe, just maybe, multiplayer.
OpenMW isn't trying to replicate the game's content — just the executable code responsible for bringing the world together. Much like ScummVM, it's also built in such a way that it could conceivably be used to run any game using Morrowind's file formats, with an editor program, OpenCS, being crafted in parallel.
This means the developers can expand the game's modding capabilities, fix bugs Bethesda never got around to patching, tweak the game mechanics and even enhance the graphics by utilising modern technology (but without having to alter the original textures or models).
A "possible" feature is the implementation of multiplayer, something fans have wanted in Elder Scrolls games since Arena and Daggerfall. With Elder Scrolls Online missing the point, I could see this as the stand-out reason to give OpenMW a bash (if/when it gets the functionality).
Of course, the project is still in heavy development, with v0.31.0 released a few days ago. If you're willing to put up with its quirks, it's worth checking out. Coincidentally, the GOTY edition of Morrowind is currently on sale on Steam; you need the original's data files to play.