Most of what I'd say has been covered. I'm going to say it again, mostly because I'd probably phrase it a little differently, but I generally agree with most of what has been said.
WM is a very very strong village. It's especially good early, as it cycles you to your actions (basically always your best cards, especially in the engines you want WM in), which speeds up how quickly your deck comes together by a LOT. It has some nice interactions with Wishing Well/Mystic/Herald. In a deck that's all actions, it's usually not much different than straight-up village. This means that later on, it tends to get weaker - but on the other hand, if you still have at least some non-actions, this helps to ensure you draw those last, which is what you want to do, as drawing them earlier gives you higher chances of not drawing your draw card. Card gets worse if there are actions you don't want to draw at some point (e.g. chapel after you're thin), but it's very rare that it's actually worse than a normal village. Have to watch it triggering reshuffles a bit, but you can deal with that, and it doesn't undo all the good work this normally does via skipping ahead. Better in games without trashing, but that's just because you lose some bonus - the trashing is still almost always going to be better than not trashing. It can do things with tunnel, that's cute, but that's not really where you want to be very often - these decks often don't want Gold, at least not much, and by the time you would get tunnel, you can usually do better.