I disagree. It opens up the game quite a bit I find. I always loved the round planets in Populous: the Beginning too.
What it basically does is allow bases to be attacked from 360 degrees, whereas most RTS's basically start you off on opposite sides of a map so there's a lot less room for manoeuvering your troops.
You need to be defending from all sides. And because of the multiple planets and orbital units, there's a lot more to manage but also to hide your commander. You can make quick escapes and re-establish somewhere else if a second planet is not colonized.
Or if you don't keep an eye on your opponent, he might have had time to colonize a small moon (or an asteroid in the future) and put some engines on it while your attention was diverted elsewhere. You'll be in for a bad time then lol.
But basically the playing field got much bigger, there's more places to hide yourself from your opponents, and there are much more ways to attack him: you could have big roaming mobs of bots, or a big tank army, you can come at him from the air and from the sea, you can nuke him, you can attack him from your planet's orbit with death lasers and such, you can colonize other planets and make them churn out massive amounts of economy and build armies undisturbed, or if all else fails you can 'simply' ram another planet into your opponents base, eradicating everything. That's a lot to take into account, and there's a ton of tactics you can use that are not available in other games.