It's a great program but if you can find a local one at a good school, it's still better to do it in person. Meeting faculty (and other students, researchers, doctoral or postdoc, etc) in a field you want to pursue for a long time and working on research with them is the main benefit of a graduate degree and is still invaluable. They will provide all sorts of guidance and opportunities over the years that you can't get online.

What are the pros and cons of doing OMSCS if one already has a BSCS?

I'm about to graduate with a BS and I will be going straight into the workforce, but I'd like to pursue a MS (without taking time off from work).

Pros: Deepens your knowledge of CS and can be used to focus on a more specialized field e.g. machine learning

Cons: Time and money investment. May be unnecessary if you just want a standard dev job.

Seconded. ~$6k for a reasonably challenging online program. Like anything, you get out of it (education-wise) what you put in, but the price can't be beat.

The other big upside to me was that I could keep working full time while studying. The opportunity cost calculation looks a fair bit different when you're giving up (less quantifiable) leisure time rather than paid work.

I agree that it wasn't all amazing, though -- some courses are great full stop, some are just bad, and many (as you say) really shine only when you go above and beyond.

Still, for those with existing programming experience or an undergrad CS degree, it may not be the best thing to do. If you want to learn some particular skillset, there are more direct paths. It might help with the resume filter, though, and it's handy for non-US people who want to get an H1B for now.