Definitely one of the best optical design software
What do you like best?
Accurate and, in some cases, very fast software for optical design. You can easily use it to optimize a design with any types of optical surfaces. Quick exports to CAD formats. Easy to update the glass catalogs. Non-Sequential mode for scatter light and ghosting analysis. Polarization calculation is average. Many modes of optimization suited for any needs.
What do you dislike?
Automation is very hard to achieve, either through Python or the dedicated Zemax language (called ZPL). It is so hard that even though I'm one of the 10 people in my University that use OpticStudio, I'm the only one who codes on it. Extensive knowledge base is available only to the elite few who have purchased support or have bought a latest license, which costs an insane amount of money for a small institute.
Recommendations to others considering the product:
Find a choice of software that matches your needs. Consider automation as a necessary thing in optical design, as well as manufacturer support, that, in the case of Zemax, you will not get, unless you pay for the license.
What problems are you solving with the product? What benefits have you realized?
Optical design and optimization. Beiing able to use the designs of other people.