It is universally agreed that Rosetta Stone kind of sucks. It's like the CrossFit of language acquisition: it makes a lot of claims that just fall short of reality. Here's an interesting article - and there are others on the site - about some of its inadequacies. http://www.casl.umd.edu/node/919
Esperanto makes (or has made) some ludicrous claims as well, of course. I'm still idly learning on my (short) bus commute because, well, why not? But I have no illusions about it. Generally speaking, the typical method of teaching Esperanto is kind of an old-school pedagogy - go over the grammar pretty much "in order" and then work through stuff until you've mastered the language - but it isn't too terrible for Esperanto because there's relatively little "new" grammar if you're used to an Indo-European (emphasis on European) tongue. But there's a surprising amount of grammar and odd Indo-European stuff for a language that claims to be simple for everybody in the world - but I'll leave that discussion to actual linguists. See also: http://riviste.unimi.it/index.php/inkoj/article/view/838/1084
So if you're wondering what to do instead of Rosetta Stone: Rosetta Stone might be good for helping to drill vocabulary or something. That's all. I've heard good things about Assimil. Pimsleur is good for what it is, but beware of thinking it teaches you all that much. All of this is quite useless without the opportunity to speak with real speakers of your target language. But, really, this is all baseless from me, I'm more of a dead languages guy and my French was always more of a reading ability than anything else (and why not, who would I talk to?).
Unless R or MATLAB count as languages, then I could talk about... something.
And another thing about the Volapuk wikipedia: one of the annoying things to me is that, if somebody were genuinely curious about Volapuk and were interested in reading some honest human-written article in Volapuk just to see what a Volapuk article would look like, it would be rather hard to find substantial Volapuk content (as opposed to machine-translated stuff).