I think it’s a very good source for information be it complex or fundamental. It has everything from basic letters in the alphabet to extremely complex science and theories. And don’t forget that it’s all based on donations. (Assuming there exists a person who donates.)
And in terms of validity and such, I believe that whatever article is there, was written by a person who values the subject and is very good at it. Why would you write an article if you have no idea what it’s about? (Minus the idiots.)
Take this scenario for instance: You’re a physicist, it’s your job. You find yourself with nothing to do, so you find a missing article on Wikipedia… And guess what? It’s about physics. You’re going to fill it in with everything you know, all the information you extract (Which is from other websites your son might claim are more valid, by the way.) It is bound to be reliable, after all, it’s your area of expertise.
Never have I once found it irrelevant or not useful in terms of research. (From my experience, obviously.)
Coming back to the idea of some people fooling around; Usually, people might decide to write wrong information in any article whether it is a science one or.. an online gaming one, shall we say. Now millions of users visit Wikipedia, per second even. And (statistically) you’d find that people who visit the more complex topics are more mature, and potentially older. This means that if they do happen to find incorrect information, or people who are just fooling around, they’ll feel it’s their job to correct it.
(Even a gaming professional might notice lack of reliability and fix it.)
I can honestly go on forever, as it is a very open ended argument from many perspectives, but I have honestly never found a better information site than Wikipedia.
Besides, aren’t other websites also written by ’people’? I’m pretty sure they’re not robots.
The only time where I wouldn’t use Wikipedia is for high level research, as I would need to extract (in some situations) the information myself.