I finished the main story missions last night. I was laughing so hard at some of the dialog that I was afraid that I would puke. I also felt very sad at times, realizing that the content in the game is too true-to-life.
However, I also loved how R* managed to roll over a decade of GTA games into a single amazingly-well-executed game. I loved all of the references to almost every single past GTA game -- especially those to San Andreas.
I just hope that if there is DLC, it contains more places (like more land masses and more interiors). Rockstar has been pretty bad about extending the playable area of such games, but this experience demands it.
In all, I'm blown away. What an amazing achievement in gaming.