Wikipedia is absolutely valuable. Better than Britannica? Does Britannica have an free online edition? Apparently they do. Some poor publicity work on Britannica's part. Everyone knows about Wikipedia, it is one of the first sites I go to when I need information. It's always a top hit on Google. Yes, there are questions about Wikipedia's editing and accuracy but I would guess Wikipedia also updates more quickly because of it's editing practices.
Although Wikipedia is very popular, it is not very trustworthy. A lot of the information on it is inaccurate or entirely false. Teachers do not let students cite Wikipedia in bibliographies because it's not a legitimate source. Anyone can edit Wikipedia pages, so anyone can write anything, whether it's true or not.