I just finished my first game on tough and it was tough.
I played head to head with the Drengin on a tiny map with everything rare. There were only 4 habital planets on the map, Earth and Mars for me and Drengi and Hoth for them.
There were 6 resources, I got a research, a military and 2 morals. They got influence and econ.
As usual I jumped out to an influence lead so I controled the UP. There was a new planet event and I voted it to myself. It was right in the Drengi system, a PQ 11. It immediately started to flip and I had to struggle for many turns to keep it but I finally got the population and influence high enough to get it out of danger.
They were ahead in tech and in military so I started cranking out 2/0 laser ships and I was soon ahead in military. As the game wore on I kept forging ahead in influence but they had the influence mine and Iit was maxed out with offense and defense. I didn't have a fleet that could touch it and they were catching up on military so I figured I was going to lose in the end.
Then I got a lucky Ranger, the first I have ever gotten in GC1 or GC2. I figured I would have to take out the influence star base to have any chance, so I sent the Ranger and a couple of Constructors on the mission.
I was still 3-4 turns away from the starbase when they declared war on me and man were they ready. They were all the way up to Singularity Drivers while I was working with Laser V and some decent armor. All I could get on a Medium hull was 5 attack with no defense or 3 with 2 armor. Their fleets were cutting through mine like hot butter.
While my ranger and constructors were trudging toward the starbase, they were pulverizing my 9/6 medium hull fleets. I was reduced to lease buying ships every turn to hold them off of my planet in their system. They finally cut down my defenses and invaded. Luckily I had 10 billion population so I lost 8 billion soldiers holding off 2 invasions.
Meanwhile, my Ranger arrived at the Influence mine and destroyed it. I took over the mine with my constructors and my influence immediately nearly covered the map. I was still at war so I could not get an influence victory . I rang up the Drengi and they amazingly agreed to a treaty for advanced diplomacy tech.
With the treaty I got a victory 10 turns later.
I have been critical of the AI on challenging for building huge numbers of weak ships (and I suppose you could say their stupidity still beat them by agreeing to peace when they could have taken me out in 10-12 turns) but I was shocked at how they sandbagged me with my supposed military superiority while they shot up the Mass Driver tech tree and came at me with overwhelming power.