Outside of taking actual Spanish classes, software packages are the most comprehensive way to learn the language. Some take the form of so-called natural learning (no grammar whatsoever), some emphasize only real-world situations/conversations (which is sort of a natural way to learn) and others throw in a mix.
Personally, I think that an adult is best served by combining all three facets together – real world situations, grammar and natural learning (see a picture of an apple, think “manzana”).
All these programs have their strengths and weaknesses but the key here is to stick with what you feel most comfortable. A little bit everyday is better than hours and hours and then burning out.