So why the applause from the developer community ? A good question and the answer, bar that it comes from Google, is that assuming you can truly appreciate OOP and Google use C++, Java and Python, you are building a real application here which will, in time, take the web to the next level.
For run of the mill sites, A2 is probably a bit too complex, but if your site is more like an application then A2 would be the way to go. We are currently writing CMS in A2.
Any A2 web-site will in effect be a complete re-write and you really have to use A2 as an IDE. In fact you don't really need other libraries with A2 [such as react or even jQuery].