Assimil is probably the most favored by me language system because of several features I find useful:
- short lessons, allowing the learner to moderate his own learning speed;
- not a vast vocabulary difference from one lesson to the following;
- using the vocabulary units in different situations (and contexts?);
- availableness of audio materials almost to all resources which could be found on the web;
- placing of the material over the book.
Nevertheless some points are not so good like:
- not always available dictionaries in the book;
- not always available grammar sum-ups in the end of the book;
- romanization which in some editions follows the hole course thus not allowing the learner to get used to the writing system used by the target language of the book.
Even though, for me Assimil remains one of the systems for language self-learning I’ve got accustomed quite much. Probably only Larousse’s Pocket Langues Pour Tous can compel for the first place, being more shorter and with more additional structures.