What it can do, what it's likely to do, and we're only in the first inning of understanding how to utilize it and manipulate it. I believe vaccines are the only medical discovery/creation that will end up being comparable in impact on humanity. CRISPR will enable us to directly, fully seize control over our evolution (we've obviously been subtly affecting that for thousands of years).
It'll take a process spanning decades for the most remarkable applications to be discovered and commercialized (or otherwise made available for the general population), and it'll be worth the wait. We'll gradually strip countless inherited diseases from the entire human race in the span of a few generations. Breast cancer? 99.7% wiped out. Parkinson's inheritance? Gone. Cystic fibrosis? Gone. The age of antibiotic resistant infections? CRISPR will solve that soon as well. And so on. As with vaccinations, there will be numerous CRISPR therapies/cures/applications that will be extraordinarily cheap, pennies per person, and deployed to all persons on earth (as with vaccines, it'll take decades of gradual generic'ization, initially all therapies will be expensive, then many will become common, and then they'll be globally deployed for pennies per person).