Different. Much less compelling.

Charlie Jane Anders explains:

The original Thrones pilot was filmed in the fall of 2009, directed by Thomas McCarthy in Scotland and Morocco instead of Northern Ireland, Malta and Croatia like the aired episode. A few scenes from this pilot made it into the aired pilot, but most of it was scrapped and redone. In 2011, producers David Benioff and D.B. Weiss told us that they watched this version of the pilot with their friends who hadn't read the books — and at the end of the hour, their friends had no clue Jaime and Cersei were brother and sister.

TL;DR: The pilot version is closer to the book, and everything feels a bit stiffer. The language is generally more formal, and the scenes go on longer and are more draggy. A lot of crucial exposition is left out or unclear, and the characters' relationships aren't highlighted the same way. The Stark family, in particular, feels way less like a real family of people who love each other in the pilot script.

Most of all, reading the unaired pilot makes you realize just how many clever choices Benioff and Weiss made in the aired version, and in the show generally, to make this huge and sprawling world both comprehensible and irresistible.

Here are 12 differences between the pilot script and the first actual episode:

http://io9.com/how-different-was-the-unaired-pilot-of-game-of-thrones-473593778