I really like the Rosetta Stone programme and I am getting on well with it. You can get a good idea of how it works from the online demos - it tries to make you learn my immersion and interpolation, NO English or any other language is used in the teaching. You get images and words, eg a new noun is presented with a picture, twice, then the third time you have to pick one of 3 pictures that fits the word - so your brain associates ‘those green or red fruit’ with ‘las mazanas’, without your other language getting in the way. It’s supposed to be how babies assimilate their first language.
It has been criticised, because adult and baby brains are obviously very different, and adults can learn in a multitude of ways. The one thing it can’t give you is rules, and if you want more structure you need to buy a decent grammar book as well, there are plenty of those around of course. I am still on level one, and looking forward to see how Rosetta is going to cope with, say, differentiating the imperfect and preterite tenses! But for general vocab, adjectives and examples, I think its very effective. One really significant advantage over other self-study methods is that it teaches spoken spanish as well - you have to repeat phrases and it compares the audio trace against a recording of a native speaker, it WONT pass you on to the next one unless you get it significantly matched! But I know that has helped my accent a lot.
You can buy it as an online system you can log into from anywhere, or an application you can use in one place offline. Either way it is horrendously expensive. You can buy it cheaper - have a good look round eBay - for one thing my copy will be listed there shortly as I have no further use for the disks other than as back ups,
Anyway I am trying to do one exercise a day after work - its about 10-15 minutes - and so far its working well.
Mx