Happy to pay for it. If I can drill into lots of data, that's a bonus.
It was bought by the Weather Channel but prior to that it was basically a big, geeky front end for NOAA and the Citizen Weather Observer Program. It takes actual data, actual meteorology reports from actual meteorologists and presents them to you. Once the Weather Channel got ahold of it they started offering numeric weather reporting; the important thing to know about Wunderground is if you're out in the sticks, and no human-tuned weather report is available to you, you might end up getting a forecast based on artificial intelligence rather than human experience (the humans almost always win).
Compare and contrast with anything that uses Accuweather, which actually takes NOAA data and fucks with it because they know you'd rather be surprised by sun than disappointed with rain. Serious. Fuck Accuweather. Also they lobbied to shut down the National Weather Service because of course they did. Also fuck Apple because the iPhone uses Accuweather.
You should also be aware of Radarscope. If you would like to know if it's going to rain on you in the next 10 minutes it will tell you. I check it three times a day. If my local radar is in Clear Air Mode, the convertible top goes down.