Dave Smith's most important achievement is leading the NRL into a new era post-News breakup, and securing and strengthening the games finances to all time high levels. Closely followed by strengthened branding, merger with Touch, increased promotion of Womens RL, and refusing to respond to News baiting.
HOWEVER. His leadership failed to address the decline on-field (amazing GF aside), continuing the trend of reactionary rule changes and poor refereeing, fans were clearly frustrated - crowds refused to improve. Smith's NRL couldn't come to a fair funding agreement with clubs, either. And very recently poured water on expansion hopes which are crucial for the games growth in the next 10 years.
Summary: Dave Smith was the right man for a specific job, and he did that while neglecting other areas. The time is right for change. Here's hoping the new leader has the balls and vision to grow, while understanding and respecting quite what it is that makes the sport of Rugby League great, rather than just the business of the NRL.