I like the mechanics of Scientific Method. SM represents a new way of thinking, and with it comes dramatic political upheaval, as the old ways are challenged by new discoveries. It represents a fork in the road of progress: do you plow ahead into the new age, or cling to more traditional thinking? The game makes that choice meaningful, by giving you trade-offs. Researching SM gives you access to Physics, Biology, and Communism, which are all extremely potent techs, not to mention it reveals OIL which allows you to plan out your modern-era strategy. Also, the first to Scientific Method has TWO great people to shoot for, the Great Spy from Communism, and the Great Scientist from Physics.
Because of these trade-offs, the world is likely to see a split between the "Enlightened" civs who research Scientific Method early and march on to the Modern Age, and the "Traditional" civs who put it off as long as possible. Both are viable options, and yield very different results.