The ModDB site is encouraging fans to vote for the best Mod of the Year. On the Blizzard games end, Diablo II has a nomination with the Median XL mod.
The main attraction of Median XL is the brand new skill trees, 30 skills per class, providing a whole new experience. The mod also offers a new base item setup with 7 quality tiers, 471 uniques, 235 runewords, a new affix pool and gem/jewel stats, honorific items and many new and powerful crafting recipes.
All this would be for nothing without the monster AI modifications and new abilities, elite and heroic monsters with even more powerful skills, and for advanced players there are 27 new uberquests based on Diablo lore and the challenges, which reward you for killing bosses at a low level or two of them at once.