The game only felt repetitive for me after 4 games.Part of this is because I find myself facing the same enemies, over and over and over.
One neutrals are active, you'll be attacked from different angles by different opponents every game. Also once different sovereigns are on, playstyles can significantly differ. As parrotmath said, add in random maps and just finding the SK will add variety.
Another part of the repetition solution is the late game, or closing in on the SK's den: it would be more interesting if, as you closed in, the SK switched to an entirely different strategy.
Instead of continuing to just shoot forth endless waves of cannon fodder, he focused his troops into mega-armies for the sole purpose of expelling you. That would be very challenging, and prevent the player from just sneaking past the hordes and going for an easy kill on the SK.
If he succeeded in repelling you, he could revert to attacking shards. But going for the shards even as you are about to topple him seems like tunnel-vision strategy.