Recently, Mark Zuckerberg made a comment saying that Facebook's mobile app based on HTML5 was "one of the biggest mistakes if not the biggest strategic mistakes we've ever made". I mean yes the application was TERRIBLE; it crashed all the time, was slow, and had a number of issues but I don't agree.
There is a number of other companies that have great HTML5 applications with just as much complexity ( if not more ) than the Facebook app. The first and best example I can think of is the LinkedIn application. This is a very nice application that performs fine with similar characteristics as the Facebook app.
Windows 8 is basing their whole marketplace around HTML5 applications. While you might argue that the computing power of a desktop is far greater than a phone, the complexity of the applications are going to be greater too.
I argue that making HTML5 applications are the way to go! Why is that?