I'd like that to be true, but I think it's still some years away from being a similar experience. Sage is impressive but still very much shows its seams: it's trying to glue together a bunch of separately developed projects, with their own ideas about things (everything from Maxima to R), and the glue is often pretty noticeable if you do anything remotely complex.
(That said, I also avoid using Mathematica for most things because I'm squeamish about ending up with any significant project too closely tied to a proprietary platform.)
> I'm just a little hesitant to do any meaningful work in such a closed ecosystem.
It's interesting. I do sometimes wonder if it's being held back because it's proprietary. Other companies have proved it's possible to monetise an open source product, and Wolfram Research is a private company so they can really do what they want in that regard. I want to see it succeed because I think it's a great product, and a very clever one at that, but I can't justify doing research that uses it when there are open source implementations I can use instead.
I wish that whenever Wolfram passes on (no offense!), his heirs will open-source it (at least for non-commercial use, not necessarily BSD-style) as a gift to humanity. (While still maintaining a commercial business-support strucutre)
I once tried to do meaningful work and, while things such as the NDSolve[] function are positively amazing, programming in Mathematica (which means using its editor) is a huge pain when you are used, say, to vim.
In the end I moved everything I had to the Python scientific stack and I'm very happy I did it.
You need to get used to the notebook concept. In the end you'll find that it's much more convenient for interactive work than a traditional command line. For non-interactive work you can still use Vim if you like.
In fact Mathematica shows its advantages most when used interactively (compared to languages, like Python, which were not really designed for this).