Can't stop ROFLing at this post. Way to completely bypass and ignore The Shivering Isles. No Unofficial mod ever rivaled The Shivering Isles.
The Shivering Isles is an expansion pack, that's different to a normal DLC or a mod.
Of course a mod created by a single person (or a small team of people) for free, in their own time when they're available, that's not going to be up to the standard of a six month long expansion pack created by a team of 50 or so professionals with many more tools, expertise that are also getting paid. However there are many mods that come close to the SI.
Remember mods don't just add quests like the official ones do. There are stunning house mods that are 100x better than Bethesda DLCs, landscape mods, combat overhauls, thousands of new armour, weapons, town and city improvements, quest lines, new areas, better visuals, textures, shaders. The majority are to a very, very high standard, with many equal or better Bethesda's standard.
For example, I'm not bigging up my own mod at all, but I created http://tes.nexusmods.com/downloads/file.php?id=34199 a while ago now. It's a mod that allows you to see the towns and cities through the windows when you're inside. This is something completely and utterly different to anything Bethesda provide, but it's something I pride myself on being of the highest possible quality. In my opinion, it's something worth having to increase the experience in game by a lot.
But anyway, the point is, whether or not you've ever used mods or not is irrelivant. You
cannot slate the wonderful community here for the sheer brilliance that is the mods that they create. Bethesda's community is simply incredible. People seem to get the wrong idea of mods as they think of hex editing or buggy shader packs. It couldn't be more different here.