What do you like best?
If you've been in the GTD (Getting Things Done) mindset, Omnifocus can keep you on track, whether your projects are simple or extremely complicated. All the details get gathered in one place, so you can see EVERYTHING that's coming up, and of course you get to set contexts for dealing with every task. Different perspective views allow you to view your to-dos by project, by context (now handled in Ominfocus 3 by tags), or my most-used view, is the Forecast View, which incorporates calendar items as well as tasks I've set. Deadlines are easily set and progress tracked. Data can flow in from wherever you have it: You can turn an email into a task in a click; notes from OneNote or Evernote can be linked to any task (and the links can be set in both directions -- go to your notes and research from an Omnifocus task, or click in the note to go back to the task). Reminders are seamless to implement, all your "stuff" is in one place so you can make sure nothing gets forgotten.
What do you dislike?
Not the easiest learning curve, but it does a lot, so I guess that's understandable.
Recommendations to others considering the product:
If you have stuff coming from all directions, nothing beats Omnifocus for getting a handle on it all. If you have used GTD techniques before, you'll love it. There are plenty of good task managers, but none better. It does have a little bit of a learning curve, but it is well worth it in my view.
What problems are you solving with the product? What benefits have you realized?
Numerous projects of all sizes can be managed in one place. We have people working with us in multiple countries and Omnifocus lets me track and proactively manage by the team member (or members), the project, the country, or overview the whole execution in one fell swoop. My personal projects are there, living happily along with everything else, and while they're easy to get to, they don't get in the way. I can certainly see the big picture at will, but can still have all I need at a click to focus exclusively on just one task, project or person. It's a convenience factor I simply couldn't live without.