This post on "level playing fields" and DMs staying ahead of players by changing the rules got me thinking about a GURPS-Fantasy campaign I played in several years back and how it ended.
The playing group had been playing 3rd edition D&D for a while and we were all pros at it by that point. We were a well drilled team of dungeon pillagers who had fallen into a successful pattern of behavior that was turning every fight into the same boring fight. Thinking it was his lack of experience with 3e-D&D and some limitations in that version of D&D the DM suggested we try something new: GURPS-Fantasy. We all agreed a change of pace looked like a fun idea.
The GM/DM had the most expereince in GURPS with one player have a fair bit of experience (but never GM'd the game), another with a little exposure , I hadn't played it in over a decade (but had played when it was man-to-man and TFT before that) and another player with no experience at all. We had 125 point characters, I lost my first character because of his bellicose ways and I hadn't grokked the GM's style of play within the campaign yet and the total newb got her first character killed as well . We both learned from our mistakes and the other two PCs kept on advancing as well.
We started to defeat NPC left and right and the DM suggested we incorporate the advanced combat rules since we were pushing the envelope of what the basic rules did well. We all agreed... the GM should have noticed our glee. In the weeks that followed we chewed through the NPCs with ever more wild and telling maneuvers and we knew what the numbers on our sheets could mean in play. The end wasn't long to come.
The PCs were on a ocean voyage from one city to another, the captain of the ship was a bit of a jerk and there was a mutinee on the ship. The GM was clearly tryign to railroad us and hadn't expected us to back the captain and chew through 30 or 40 opponents in 30 seconds of game time. The ship understaffed after the failed mutiny ran aground on a mysterious island (which by some odd chance the GM had mapped out and well-detailed). Our brave band of PCs were exploring the island while the captain and remaining crew were trying to build a camp and repair the ship. w/e came across soem ruins and a cave... and out came a Giant!
Now Giants in GURPS unless total dweebs are a horrible opponent for a small band of GURPS characters and things looked grim for our band of 150-180 pt characters. The GM clearly expected a fighting retreat. We instead rushed the giant who took a dagger in his eye, a crossbow bolt to the neck, an axe blow to the knee which sent it crashing to the ground which was immediately followed by my swordsman making a ridiculous leap and stabbing the giant through his other eye and into his brain killing it. The fight was over and the DM/GM threw his hands up in the air and declared "that's it I cant challenge you guys anymore"...that was the end of the campaign.
The GM had made some mistakes, he wasn't as good at math as we were and he wasn't four other people with several years of game experience between us who all started reading GURPS as soon as we agreed to start playing the campaign. Trying to beat us or keep us in check by changing the playing field from 3e-D&D to GURPS and then employing the advanced combat rules in GURPS just didn't work out for the GM. We all moved onto something new after that and the DM/GM didn't get to keep running a campaign.