PC gaming is inarguably made better by great fan-made mods, and the large-scale work done by the people at TESRenewal are a shining example of that. The group that's working on Skywind--the community project that's recreating The Elder Scrolls III: Morrowind in The Elder Scrolls V: Skyrim's engine--has released a teaser trailer for Skyblivion, which does the same with The Elder Scrolls IV: Oblivion.
Watch Skywind, The Skyrim Remake Of Morrowind
If you haven't checked out Skwyind, I recommend you do so at the link above. The project is ambitious and impressive, and they're still working on making it complete. There's environments and textures, but the team is still adding the quest lines and dialogue (much of which they're re-recording).
Skyblivion is following the same path, though with a much smaller team. Aside from those planning the endeavors, the teams on both projects are just volunteers who have skill or time to offer towards the project. The more people can contribute, the faster the work will go--so if you think you can help out, head over to the forums and sign up.
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Skyblivion has been worked on since March of last year, and it looks great so far. Oblivion was an attractive game when it came out, but has definitely aged since then. Skyrim's engine was gorgeous, even if it had some problems of its own, and the game looks much better for it.
Oblivion's Cyrodiil was a much more lush and bright fantasy environment than the titular Skyrim, so the locale is pretty easy on the eyes with better graphics. Stay tuned to us for more updates on both projects, which will hopefully see a full release in the not-too-distant future.