Pros
Robert Half is a massive company with a well known name. They know and understand recruiting as a company and through their training programs you'll learn recruiting as well. They are a company obsessed with numbers, so as long as you maintain those numbers, they'll most likely be pleased with you. If you make it at Robert Half you'll most likely be able to find a Recruiting Job anywhere else you apply. It's a good company to work for if you fit the profile.
Cons
They are a company obsessed with numbers. This can become very stressful. I started with Robert Half right before the economic downturn and watched weekly as employees all around me were "let go", Robert Half's way of laying off without severance. Management was constantly threatening the Apocalypse during conference calls which did more to depress people than motivate them. There isn't much of a work-life balance, my average week as about 60 hours, and that was nothing compared to some of my colleagues. Robert Half is a machine, albeit a well oiled one, but it isn't a place that will take time with you as an individual. You are just a cog, and if you don't fit right, they won't hesitate in dropping you.