The enemy air units are what always get me. I can handle the ground units as for some reason the skirmish AI seems to like simply massing T1 assault bots which are easily taken out by half their number in Mantis, or even just 3 rhinos. The problems I've been having are coming from the enemy T2 gunships. My interceptors can take them out, but they run out of fuel and ammunition and it takes forever to rebuild if you don't have a refueling pad.
I've been quite enjoying my time with the demo so far, but I still have a lot to learn. It's really quite different from a lot of other RTS games. The economy isn't just "set it up and forget it" like most others. The basic mass extractors need to upgraded whenever you get the opportunity. Mass extractors are by far much better than mass fabricators. A T3 mass extractor is a huge target. For almost no energy expenditure you get 12 mass generation compared to a T3 mass fabricator which generates 24 mass, but also uses 1500 energy. The AI seems to have it's priorities straight at least in that it is targeting my resource production before anything else.
So far I've lost three games in a row to the hard skirmish AI, all for different reasons. The first time I lost was because my commander thought he could take on a monkeylord by himself. My commander did indeed kill the monkeylord, but only because his destruction unleashed a nuclear blast that leveled 3/4 of my base. I wasn't prepared for any experimental units as I'd tried to build one against an easy oponent, but for some reason it would let me even though I had T3 engineers. My second game was lost because I couldn't keep my economy running with the constant attacks by enemy gunships on my mass extractors. Finally, my most recent game I tried establishing forward defensive locations at the "chokepoints" with shield generators, but I lost one of those locations when I couldn't get any air defenses up fast enough to counter the enemy gunships. Once the shield was down the enemy started marching through with T3 assault bots and I decided to quit. It felt as though I was only delaying the inevitable. I may have been able to win if I had stayed and attempted to finish my own monkeylord, but at that point I only had enough resources to finish building it or to switch over to base defense. <_<