The web industry is very dynamic, much like any of the IT fields
out there. It's not just about HTML and stuff, the website you
create needs to be very dynamic, user-friendly, yet at the same, do
what it's supposed to do.
This includes the usage of several web technologies like
JavaScript, Ajax, streaming multimedia, web server technologies,
etc.
The web industry has progressed a lot since it has borned. From
static HTML pages, to incorporating CSS to make the site nicer, and
to now Web 2.0.
Ask yourself if it's really something you want to do. There's a lot
to learn for Web, sometimes you basically have to unlearn what
you've learnt.
HTML is easy, but if your HTML coding practices are bad, once you
move on to a newer web technology, say XHTML, you will find
yourself re-learning everything, as well as unlearning
everything.
If it doesn't unfaze you, then you can consider it. It's one of the
best fields out there if you know your stuff well. 
