A good start, but no substitute for a brain, a teacher, and live communication.
I'm a qualified ESL teacher so I know a thing or two about teaching and learning languages. I am currently using Rosetta Stone to learn Farsi, which does not use a Latinate alphabet. I read loads of negative reviews and positive views before I made the decision to buy the online version for 6 months. The reason why I went for the online version was because I did not want to be stuck with an expensive beermat if the CD got scratched or my computer needed upgrading, and if I haven't learned much in 6 months (the online version goes up to Level 3) then I have spent £120 and not £259.
The nearest Farsi language class to me is in London, and I live about 2 hours from the city, but my partner is Iranian so I figured that the online programme, plus a second language environment at home would be cheeper than paying the cost of the language class and travel to the city. I think this is something to be aware of – a language class in a college, which will focus usually on a grammar-translation method, will cost you more over 6 months than this programme will.
So what's great about it? Well, communication methods of language learning focus on absorption and retention and getting you to think in the target language, rather than to translate it in your head. The pedantic, carefully graded exercises are incremental and gradually build up grammar by feeding you vocabulary words and getting you to notice the surrounding grammar the sentences.
The speach recognition sytem used throughout helps you retain the language and is good for correcting your accent, although sometimes the programme will not let you progress even when you are pronouncing the word properly (this can be a bit frustrating).
Generally, the programme is fun, easy and intuative to use, and you can do as much or as little as you feel like, which is also a plus.
You are forced to think about things and there is enough repetition of the exercises to mean that you return to grammatical structures. You CAN guess the meaning with some exercises. I am not unduly
concerned about this. This is almost inevitable in any language learning environment because we are always looking for the familiar. However, repetition and retention are designed to help you retain your vocab and develop an instinctual feel for the grammar. So even from the start I can tell this is a very useful tool which will work. However, it is no substitute for a brain – you need to choose to use their exercises to notice things about the language, and this does require some effort on the part of the learner. Which is always the case if you want to learn something well.
Some caution is needed though because Rosetta Stone is not a perfect system. Although I have not tried this for my second language, Spanish, I can tell that progress will be faster for speakers of languages which use a Latinate alphabet, such as Spanish or French. There are issues with the reading and writing sections of the Farsi programme which I suspect are shared with Arabic and Mandarin – essentially this programme cannot teach you the calligraphy you need to be able to read and especially to write well in these languages. Writing is perhaps universally neglected skill in language learning but it does highlight the programmed limitations. I am supplementing Rosetta Stone with the excellent tutorials from www.easypersian.com which are totally free but also incremental and focus on how to form your letters.
The other issue is of course that it cannot replace live speech and communication or contact with native speakers of the language. In particular the formal written Farsi taught in Rosetta Stone is different from the everyday speech. Of course, one must learn the written version first as a learner, but the fact that oral farsi is different from “book farsi” is indicative that nothing can replace live speech.
I suspect, though have not tested this, that the programme is more useful from elementary to intermediate levels and in a second, rather than foreign language environment, This programme is great if you are in a second language environment (as I am at home) or in your target country and need quick tools to acquire vocabulary and basic grammar fast.