It has such an extreme changelog, that I won’t even try to summarise it further, find it at the Nexus site, however I do want to quote a single Q&A from there:
I highly recommend starting the game with SkyRe immediately, as you will have to create a new character to really experience it, and you won’t miss anything by installing it in the first place. Skyrim Redone is a complete overhaul of the game, with a modular construction and professional level concept. Combat become boring, enemies become unbearably weak, and you can become the head of any guild by a very low level. Also the races are boring (ability-wise) with clear winners and loosers. Skyrim has an interesting perk system with some great ideas… however, if you know CRPG / RPG games, or played with previous TES games you’ll feel it isn’t so sophisticated and refined as it could be.