Things that work. Things that improve life for the world's masses. Personally, I love to make things, and take great delight in the process of invention that leads to something that finally works. It seems, though, that most young engineers graduate convinced that their education is over. After four or five years of struggling through differential equations and organic chemistry, they just know that studying is yet another of life's unpleasant obstacles they've finally overcome.
Embedded design is a dynamic field that changes daily.
Yes, it's possible to find a comfortable niche where you can park for a number of years, ignoring the advance of technology. When it's time to hit the job market, though, you may be shocked to find everyone speaking an incomprehensible language. Generally the best courses are those offered by vendors. Any successful vendor is pushing the very latest technology, and many recognize that they simply must offer some sort of training. Probably the best way to stay current is to read constantly and widely.