Five hours in and I still haven't annihilated a planet. I may be getting closer, though. I actually saw a structure that could do such a thing in my build orders, but the strategic situation was not quite right to use it. So far, it's simply been much more efficient to win the game with a huge wave of basic units, which I suspect might have something to do with the fact that I'm playing on the easiest difficulty ("Normal"). The AI has not been especially aggressive, and I've wound up running away with all of my matches thus far (except for one, where I spawned on the same island as the enemy commander, and then the game didn't pause correctly when I went to the bathroom, so I was killed while I was away from the computer).
I really want to see the high end stuff, though, so I may have to either kick it up to a higher difficulty or just toy with the enemy while I mess around with superfluous building. I don't like the latter plan, because it reeks of hubris, but ideally I'd like a chance to explore the tech tree while I'm not under fire, so I can get a comprehensive view of what exactly you can do.
I have to say that despite my reservations, I'm actually enjoying the game thus far. The fact that I have an uninterrupted (embarrassing outlier aside) winning streak helps. I'm not sure galactic war is the best introduction to the game, though. There are all sorts of gaps in what I can build, and I don't know whether they'll be unlocked with future technologies or whether they're simply blank spaces in the UI. I also get the feeling that my limited toolset is deforming my approach to the game. You probably don't want to build a massive fleet of basic tanks to deliver an early rush in a more typical match. I imagine against a prepared player, that's just an invitation to waste a huge amount of resources.
Still, I'm going to stay the course for now, and try to finish my current galactic war. There's something immensely satisfying about having a force of 600 tanks at your command, even if it's so far proven to be gratuitous overkill.