No one tool is going to do everything. Flashcards are actually pretty good for acquiring masses of vocabulary. But it doesn't help you put those words together coherently or even enable you to comprehend what you hear.
Language acquisition is all about growing a set of extremely complex interconnections between brain cells. You need to grow a massive number of interconnections between many areas of the brain (including to sensory and emotional areas) and you need to strengthen those connections by repeated firing.
Software, books, audio and video can play a supportive role but there's a big chunk of the brain development that is only going to come from struggling to express your own mind and to interact with real people in real time.