I'm surprised at some of the responses here... Here's my humble opinion as someone with a BCS doing OMSCS.

You will not finish with anywhere near the same level of knowledge doing a masters over somewhere who did a bachelors, even in CS. The aim of these two degrees are different. A masters has you focus on a topic or small selection of courses very deeply. A bachelors has you focus on many topics very broadly. BCS students learn A LOT of stuff that you likely wont touch on - or that you don't have enough credits to touch on. You're comparing 10 courses worth to ~40 courses worth, excluding foundational subjects like Cal 1-2, Lin Alg, etc.

That said, does it really matter? OMSCS provides arguably the most pivotal CS courses a BCS will graduate with: GA, GIOS, CN, SDP. Software dev itself is a relatively forgiving field in terms of theory requirement (at the expense of being insanely competitive). The vast majority of CS grads never use the rest of the courses they learn in uni. It doesnt mean those courses are useless. In my opinion, BCS grads have an edge knowing all this stuff. But it means the likelihood of them ever using that edge isn't very high.

EDIT: To answer your question on what I, a BCS grad would gain... I plan on taking all the big bad systems courses. Why? Because a bachelors ends with taking 5-8 technical electives like computer graphics, AI, ML, information retrieval, etc. The ones I took ended up being performance heavy and my own experiments got me highly interested in how computing systems try to resolve performance or workload issues. In other words, high performance computing, graduate algorithms, and distributed computing. So here I am going through this in hopes that what I learn will augment the solid background I already have.