Normally, if you want to analyze a microbe, you do it by culturing the organism in Petri dishes. By varying the growth medium you can find out a lot about your organism: what it eats, if it breathes, how it metabolizes various things. The problem is that only 5-10% of bacteria grow on plates. Microbiologists call this the "plate count anomaly" and what it means is this: your sample in a microscope could be teeming with life, but if you plate it you'll probably get this homogeneous little sample of not very many organisms. The rest are called "microbial dark matter."
With metagenomics, we could see them all. It made people a little funny in the head. You might remember that "The Microbiome" was a big idea in the media for a while. It got pretty flattering treatment, considering what it is: a mass of mostly proto-shit floating around inside your colon. But the enthusiasm wasn't too far misplaced, because a major area of biology is growing by leaps and bounds now.
If you are a computer programmer considering a career change you should really take a day off to look into the new genetic technologies on offer. Performance is doubling every year [1]. The world is changing. And computing is at the center of it, both practically (all that research generates a lot of data) and conceptually (because gene expression is information processing). So give it a look.
[1] Remember that? https://en.wikipedia.org/wiki/Moore%27s_law