Great culture, great opportunities, great process
Pros
Hanover is a real meritocracy. If you excel, you will get raises and promotions quickly. Most managers actively help you plan your career. If you want to go to grad school they'll hell you strategies on applications; if you want to stay long term, they'll give you opportunities to build skills and get promoted. Which leads to another point. On the research side, you will gain hard skills that are easily transferred to grad school or other companies. Hanover makes a point of training researchers well, and excels in this area. As a researcher, you learn a ton. The random and interesting topics you become an expert in are legitimately valuable, professionally and even socially. The work requires you to focus and learn, and it's really intellectually rewarding. Finally, Hanover does a fantastic job of building strong processes to train, deliver feedback, and streamline production. This helps keep things running smoothly, helps you to know where you stand, and overall makes the hiring, orientation, and day-to-day pleasant and efficient.
Cons
On the research side, it's really fast-paced. You need to be OK with ambiguity, best guesses, and trusting your gut. If you want to get the perfect answer or spend weeks on a topic, this is not a good place to work. They provide daily free snacks, and frequent free breakfasts and lunches and happy hours. It's easy to gain weight, because the work is sedentary. The 401k match is mediocre.