I have two memorable stories I can share (I have a couple more, but I don't want to make a massive post). The second one is the most awesome, and shortest but I'll save it for last
First story: I was playing Sword of the Stars (a 4x turn based space strategy game if you don't know it), and this was my first ever time playing it. I had managed to build up a powerful fleet, and had pushed my opponent back to his last couple planets in the far corner of the "galaxy". Victory was all but assured at this point.
Now in SotS research is a big part of the game, and I was currently researching AI which added lots of bonuses to things. What I didn't know is that, just like in real life, things sometimes go to shit at the drop of a hat. Basically Skynet happened. I got a prompt saying one of my planets was taken over by the Rogue AI. I sent one of my token defence cruisers to check it out as basically all my ships were in one fleet on the other side of the galaxy attacking the enemy homeworld.
I expected to sort the matter out quickly, but when my cruiser arrived at the rogue planet it was greeted by 8 smaller ships which promptly destroyed it.
The next turn I saw the AI was sending a massive fleet it somehow built directly at my homeworld. I had 2 outdated ships defending my homeworld (along with a couple defence satellites), and my fleet was too far away to get there in time, but I sent three of the fleet's fastest and most advanced battleships to intercept in the hope of retaking my doomed homeworld after the inevitable defeat.
The enemy fleet arrived with 12 small, but tough attack ships and 3 cruisers. I had one old cruiser with outdated tech, and a small scout ship built for range not battle.
I was doomed. However I was to be surprised. My scout ship was lost in the first wave taking out two of it's enemy counterparts, but the cruiser managed to hold on. By keeping on the move and taking advantage of it's superior long range attacks it managed to weather FOUR TURNS worth of battle. By the time my battleships got there the enemy fleet was almost totally destroyed, and that plucky little "cruiser that could" survived it all.
In the end that cruiser and the three battleships went to the rogue planet and turned it's surface to molten slag with giant lasers
My other story is shorter (thankfully), and it is one of the greatest gaming experiences of my life. I used to work in a cinema, and one day we played DEFCON on the massive Cinema screen. A giant 20ft wide digital screen with powerful 5.1 DTS surround sound. It was like being at NORAD as we defended the US from a Soviet Missile strike.
If you've never seen DEFCON here's a screenshot:
<img height=400>http://www.lgdb.org/sites/default/files/screenshot1_5.jpg
Now imagine that in a darkened Auditorium on a Cinema screen. Breathtaking.