Endgame Fantasy
While playing against the bots, I noticed a distinct lack of an end game fantasy situation. I could never built my fleet of battle cruisers or my giant blue ball of archons or my lumbering wall of siege tanks. No matter how long the game went on for, I was still stuck playing with marines(which was what basically all the tier 1 ranged units felt like) with at most 2 or 4 of whatever interesting unit my squad allowed.
Most of my favorite moments while playing RTS's, especially in large team games, come from these end game situations where giant armies of super units with crazy abilities are clashing. Without that to look forward to, games tended to drag, and getting close to max felt like some kind of terrible deadline I wanted to avoid, even though, the games were quite enjoyable up until that point.