LucasArts and Totally Games' Star Wars: TIE Fighter is still one of the best space sims ever made despite being 25+ years old, but now, after "years in development", it has been modded into X-Wing Alliance - which wouldn't be impressive, given that Alliance came out in 1999, except the results are incredible.
Even though this is technically a case of a 1994 game being modded into a 1999 game, it's done via the X-Wing Alliance Upgrade project - which is a still-ongoing effort by a team of modders to completely update Alliance to look like a modern game. Pretty much every model, texture, and background in the game has been overhauled to incredible effect.
Now a separate team of modders has put TIE Fighter through this project, and the results look impressive, most impressive. It includes all 13 original campaigns, with the first eight being "reimagined" with new ships and missions. Including training levels, the mod boasts a total of 145 missions that have all been gloriously overhauled with the X-Wing Alliance Upgrade mod.
RELATED LINKS:
TIE Fighter's greatest campaign: the Sepan Civil War, and benevolent imperialism
TIE Fighter-inspired animated short is visually amazing, an affront to historical accuracy
TIE Fighter and my new hope for the Star Wars universe