Fog, drizzle, and hard rain can improve your chances at stealth, duststorms can virtually destroy visibility altogether, and nothing quite says 'hell on earth' like traversing the Glowing Sea during a heavy radstorm!
Not only is it an audiovisual feast-describing it as merely 'pretty' would be misleading-but its effects will definitely change the way you play. Weather overhauls have always been a big hit for Bethesda's sandboxes, and this upgraded port of the popular Skyrim mod is, hands down, the best I've ever seen.