Well, I will start with the science/physics: they both use what Sir Isaac Newton discovered...GRAVITY as well as Positive/Negative G's
Psychological: Nemesis uses the fear of being in a crater in the ground to create an atmosphere more of fear were as Smiler uses Joy (the average public don't tend to know the theme) against you, giving you fear of permanent euphoria
Marketing: From what I have seen, the Nemesis ads/campaigns concentrated more on the theme of the ride were as The Smiler's campaign's were more about the worlds first 14 loop coaster, not sticking with the theme that originated with the scare maze directly linked with The Smiler's
Intro to the ride? I am guessing that is what it is...not my place to say, not an expert on that subject, sorry...
Business: Again, not my cup of tea, but Nemesis had a budget of £10.000.000 and manufactured by Bolliger and Mabillard, where as The Smiler had a budget of £18.000,000 and was Manufactured by Gerstlauer ( I think I spelled that right
I hope that I was of some use, and good luck