Navigation on the web sucks. Large websites can be hard to use and oftentimes send you to the wrong place. Most e-commerce websites I use are terrible at navigation.
As it currently stands maintaining separate location tools, in this case a main navigation and search on websites usually means one gets neglected as we think we have covered how to get to the content.
I have always been more search-dominant so if a website has a good search tool, i'll use that over a mega menu.
Amazon get's it right in my opinion. You select the category you want, and search for what you want.
Another great example of search would be Vans. Their search is simple to use and easy to find. Their categorisation of products is also easy to follow so I have more options.
Search over navigation makes much more sense to me but I'm aware this isn't a catchall solution as people will habitually search for books, games, DVDs and CDs so products work (like Amazon and Vans) but possibly not pages, at least not yet.
I would love for a large product based website opt for search over navigation and it seems I am not alone in this thinking:
I'd be interested to see a large ecom site with hundreds of categories drop their main nav in favour of sophisticated search.— James Seymour-Lock (@JamesSLock) July 16, 2015
I don't know the future of navigation on the web but I think search will play a large part.