I have two, one a fight with an AI, another a fight with other players.
I have AoE3, which is based during the 1600-1800's, and I was playing on the Amazon map. I liked playing on this map in paticular because there was a river that cut the map in half, and if you controlled that, you essentially controlled the map. I had two allies, but they didn't seem capable in crossing the river (they had big ass armies, but just didn't want to land. Probably an AI issue), so I had to do most of the heavy lifting. Once the river was secured (didn't take long, the AI doesn't realize how important it is to secure it immediately), I built up my economy. Got hot air balloons to scout the enemy base, and for another reason that I'll go over soon, and had my boats patrol. There was the occasional case where they managed to make a ship, but my navy was vastly more powerful and numerous.
Once I made in to the Fourth Age, I made monitors, my favorite unit in the game, which can bombard buildings and units from a very far distance. I had effectively everything but a small sliver of the map within range, and I was full well ready to use them. After taking out their outposts and such, I began getting ready to land a force to set up a forward command, making multiple barracks, artillery foundries, and a Fort, which would defend against any counter-attacks. Then it finally happened, they no longer had their town within my range. They had slowly built farther and farther from the river, their town was destroyed, no longer having a towncenter, but they had an army, and they wouldn't surrender without a fight. I looked at what they had, and they had at least 50 culverins, a type of cannon designed to destroy ships and other cannons (the latter reason being why I almost never use them). I probably should have made an army of cavalry, but I assumed they wouldn't last long, so I made an army of 100 musketeers. Culverins didn't have the same aoe effect that other cannons did, so I assumed they wouldn't win. I sent my army to take them out.
"Any last words before I destroy your army?" the enemy AI said. They make threats and such whenever they see your army. I had them say this before, when it was them that were destroyed. Bu this time was different. I launched the assault, but the cannons kept moving back as soon as I was within range. My musketeers were dropping like flies! So I had no choice, but to send them into a bayonet charge. Only about 30 survived the charge, but the cannons became less effective. When my army was dead, their army wouldn't last long. I made a standard army of cav, musketeers, and falconets (standard cannons) and charged their position. They didn't last long, but that fight made me realize how good AI can be when it came to micro managing.
The second story is much shorter, but it's the reason I no longer play Halo Wars with other players. My friend and I got another friend to join us, and we decided to play multiplayer 3v3. An enemy warthog scout went next to my base, and I noticed the distinct glowing line of a mac blast. Then another. Then another. Only one was necessary, but my base was struck and immediately destroyed. I lost within the first 90 seconds. We left shortly after that. We never played again.