It's pretty basic. On the left and right sides of the map (space tileset, 64 high, 96 wide) there are 2 Xel Naga Temples surrounded by walls. Kill the opposing team's temple for the win. In front of the temples and above them and below them are spawning points. The players who own the temple command the forces that are spawned at these points. They auto-attack to the other side of the field. Kinda like Star Wars Coruscant, or Cerebrates. Unlike the othee two, you get money for kills. Every 2000 points=8 mins for the bases and 600 points for the heros. Heros get to choose from 1 of 6 units every time they die. They help their team fight across. With the minerals I mentioned earlier, you can upgrade your army.
Now, where does the strategy and competition come in?
When you first play the game, you'll find that tanks are probably the most important unit. Sieging them in the right place or letting them auto-wander off and get killed with the rest of your army is the difference between life and death. You'll then learn that the most important upgrade is vehicle weapons. So now each player is siege-whoring and it's a stalemate. This is where there's competiton.
In each of the short paths between their bases there are small hill-like terrain features. Siege tanks on those for a defence point. There's also an island in the middle. If you manage to beat the enemy back into their base (have your heros use the firebat or marine for massive killing) you can siege on their side of the middle hill such that the tanks will fire down on their middle spawn point. With that, it's GG to them. But, this can be prevented. There are only 8 detectors in the game. 4 missle turrets, that can be killed, at each base. This makes ghosts as valuble as tanks in the long run. Ghosts have cloak at no cost (they just get the 1 energy reduction every second) and lockdown at 40 energy. By locking down enemy tanks the rest of your army can avance a little bit and shtart killing some of the tanks.
Ok, so now it's a lock-down fest. No detectors lets them do whatever the fu¢k they want. But then there's vultures. Because this requires a deal of micro most players don't do it, but by putting mines around your tanks you can s¢rew the ghosts over. It's tedious and time consuming to do that, but it's highly effective, as the mines do outrageous amounts of damage. This naturally leads to the idea of suicide ghosts where the heros would take a ghost and deliberately walk towards the enemy tank and get right up to them, because it takes a few mines to take out a hero ghost.
Beyond that, the only thing I've noticed is that after a while of tank upgrading you'll want to give the infantry some armour so that they'll last longer and are bale to get closer to the enemy. And with that, I've not yet had an opponent who could challenge me enough to come up with another idea.
Basically it's simple, and unwinnable if you get stalemated, but I enjoy being stuck and trying to find a way out of a tough spot. That's why I like this game so much.