I loved the thinky bits of Inception, and the team work bits, and the magnificent visuals, but not so much the overall movie (and especially not the Dom & Mal Show that was meant to be so tragic and heartstring-tugging), so I wasn't entirely invested to the point that the HA HA IT WAS A DREAM ending made me want to bitch-slap the director. I did stay to the end to see if the top would fall over, and expected it to, but it didn't and I just shrugged at what seemed to me to be an invalidation of what I just spent a couple hours watching.

OTOH, the BtVS episode "Normal Again" is pretty much the straw that broke the camel's back for me with that show -- the final scene of that episode invalidates all of BtVS because it leaves us with the inescapable conclusion that Buffy Summers is a catatonic patient in a mental institution, dreaming the show's action from day one. And it's funny, because nobody in the fandom really ever talks about it! But that's when I pretty much walked away from the show.

On the third hand... ;) There's a movie called "Total Recall" starring Arnold Schwarzenegger, and here is the IMDb summation:

When a man goes for virtual vacation memories of the planet Mars, an unexpected and harrowing series of events forces him to go to the planet for real, or does he?

...and I swear, the only thing that could have saved that stupid fricken movie for me would be if the final scene was Schwarzenegger's character fighting his way out of the machine-induced virtual vacation that was the entire utterly ridiculous and morally bankrupt movie, to see Sharon Stone's worried face as she tells him that they'd almost lost him and the ambulance was on its way. Stone played his wife who, in the "dream" that was his programmed virtual vacation, was actually a government agent sent to watch over him to make sure he never got his memory back, according to the logic of the created world. When his "memory" starts to return, he has to kill her before she kills him, so he essentially shoots his wife in the face during his "vacation." And that wasn't even the most egregious thing that happens in that movie. That plot *needed* to be invalidated! "It was all a dream" was the only thing that could have made it work for me.