From 2001 to 2003, I played the majority of my golf on a course that had firm, undulating, but only moderately paced greens. The course was relatively new, and the greens got a bit softer each year, but they were still pretty firm when I stopped playing the course regularly. You had to play run-up shots on most holes unless the pin was in the back of the green. The undulating greens made the approaches, chips, and bumps a lot of fun to play.
In short, based on my only experience with firm and undulating greens it was not a bad thing. I could see it being more problematic if the greens were particularly fast as well.