Usually, people refer to the Ultimate series by this publisher. Nowadays, the company focuses mostly on their new multimedial series and seems to only reprint (at best) their successful and high quality Ultimate series.
The Ultimate series usually consists of two levels/volumes with CDs: Beginner-Intermediate and Advanced.
The lessons are based on dialogues and their translations, similarily to Assimil but longer. Follows vocabulary and grammar explanation and a few exercises.
Among the strengths are: systematic and clear explanations and audio.
Opinion on the dialogues vary. Some consider them doing the job well, others find them too boring.
Among the weaknesses: Not too many exercises, some of the courses may be slightly dated.
Reviews and discussions on HTLAL:Edit
comparison with Assimil (LL loses this battle)
an informative thread on various aspects of Ultimate using comparisons to other courses and the Ultimates in between each other as well. Points out, among other things, problematic approach of LL to teaching foreign scripts. Positive and negative views quite balanced.
Individual courses reviews:Edit
one of the threads on Ultimate French (a positive one)
xylophagous' log featuring Ultimate Spanish but nearly at the end and more like a short review than a comprehensive experience log
The new courses: Essential, Complete and Platinum editionsEdit
Haven't been much reviewed by the HTLAL members yet despite several posting about their intentions to buy the courses when they were hot news. The publisher on their website highlights the multimedia aspect, convenience, apps for smartphones and tablets and so on. There is no official information on the actual level the courses lead to, no approximate word count and so on.
Review on HTLAL:Edit
by delta910 and others in 2011 when the courses were being released
by Cavesa in 2013
Third party reviews:Edit
Michael Bateman basically excited about it but vague about results
New York Times about the app excited, perhaps paied