When I started gaming I was all up for the complicated rule systems as I was a fan of the games as being as realistic as possible.

I was going to suggest Phoenix Command but that’s not a proper RPG rather a replacement combat system which leaves me to consider another candidate and I can’t really choose between either of them.

So I guess the most complicated games I own are Earthdawn and The Babylon Project.

Earthdawn.

On first glance the game appears to promise so much in the way of background; which it has in spades and a unique resolution system which is where it gets complicated.  Trying to keep track of all the different values and the different die types is a real pain in the behind.

The Babylon Project.

I loved Babylon 5 and I when I heard of a licensed role-playing game I had to have it, the downside was that at the time it was only published in the US; luckily I was going on holiday to the US that year and tracked a copy down.  The game has nine or ten stats and a very complicated combat system.