First off, i dont get to learn any of the factions to a comfortable level. Im constantly thrown from race to race and only have 5 missions for each. This created a miserable experience for me.
Secondly, there never was any challange. I am not restricted in how many elite points you can spend and are not pressured in any meaningful way. Completing a mission didnt feel rewarding, it felt exactly the same as the previous missions.
And thridly, you dont get to experience the full story of either faction fully. This was the dealbreaker. I complete a mission, another faction progresses the story without my involvment. I felt disconnected from all the factions and felt like i was watching a movie not playing a game, and just watching the story unfold rather than experiencing it myself.
I pray to the god-emperor of mankind that with the necrons comes a dark crusade/retribution style campaign where i choose a faction, and take in its story to the fullest. I dont want to feel like im forced to play eldar if i find SM story arc more intresting.