...it's the way the ending was implemented.
Battle Readiness high or low? Doesn't matter, same cutscene.
Geth or Quarians alive? Doesn't matter, same cutscene.
Rachni queen alive or dead? Doesn't matter, same cutscene.
Renegade or Paragon? Doesn't matter, same cutscene.
Regardless of plot holes and deux ex machina, what pissed me off was that the last 10 minutes of the game was antithetical to the way the entire series - hundreds of hours of playtime - functioned up to that point. The whole frickin' point of Mass Effect was that your choices mattered but ultimately they just didn't. And the fact that choosing control, destroy or synthesize only ended up changing the color of the explosions (okay plants had circuit boards in their leaves if you chose synthesize) was a fart in a bathtub.
I had a Paragon save and a Renegade save from Mass Effect 2 and played the Paragon first. There is no incentive whatsoever to play the Renegade save. I'm not even interested in any DLC because it's all pointless.