Batman Arkham origins has the odd slowdown when facing dozens of enemies, but for some reason it makes the combat seem cooler. You can see all of Batmans fancy moves and counter attacks, and the animations are beautiful, i can see where you are coming from with this.

Sometimes I'm not sure if it's intentional or not :s

Yes, especially in old shoot-them-up (Thunderforce, Raiden, etc.), when there is so much on screen it starts to slow down, it even increase the impact of the scene, the feel that there is so much on screen, and in fact it it even add a welcomed relief to the gameplay very similar to a slow motion. Slow motion is a trick that is quite used in movies also, where there is no framerate issues, because it make feel the action more powerfull. Especially in old movies, but you can still see in Pacific Rim for example. Unstable framerate are used quite a lot also, just see the Gladiator movie. A game were it's very noticeable it's on purpose is God of War, the action is nearly stopped on impact, but in fact in this case there is no framerate drop.

But especially, to get closer to the main topic, when the game still  feels optimized with an average good framerate and good graphics, it's like if the scene was "too powerfull for the console to manage", and that for me it add some magnificience. My best example would be The last of us on PS3, it's not like the team was lazy or had a tight schedule, it feels like they wanted to give the best scene they could, a scene so good that even with overoptimized software the console could not manage, and it added some magnificience to the experience... for me. I mean, I like it as a proof of how much they wanted to deliver, not just be bond to the hardware limitation and go outside of an comfortable framerate.

There was a tennisman I loved a lot a long time ago. Once, he played a match after he got a wound, he was having so much of a hard time just to run, but he played for 5 straight hours, all in sweat, clearly in pain... but he prevailed, that was such a great match ! That the same feeling I get from a great game suffering a framerate drop when displaying a great scene lol

The slight slowdowns when Bayo's big punches and kicks land always felt like they had more weight.

Infamous second son when using the ultimate neon power

Well frame rate drop equal to headache on my head :p, seriously especially first person games and some action adventure game that require rotating the camera and suddenly you want puke. You have to differentiate between slow motion and low frame rate lol, even high frame rate slow motion is better then low frame rate slow motion :) .

Xenoblade comes to mind, in one way the FPS drops were annoying, but after a while it somehow started to add a cool feeling, as if it was slow motion or something, epic! :D

When Doom 3 released, I'm completed it with geforce FX 5200 on low setting, it still barely ran above 25 FPS. Years later, I played it on normal PC and couldn't stand it. Playing Doom 3 at framerate above 30 is just wrong, makes you notice how really bad combat in this game is.

This reminds me of space invaders but in reverse. The aliens all start out slow and gradually speed up as they are killed off, but that dynamic wasn't by design initially. It happened because the number of enemies on the screen at the start overwhelmed the cpu, so as you killed them off it freed up memory which sped up the aliens thus making the game harder and more interesting.

I did the most construtive post to the thread.

Framerate drops are bads and don't add nothing to the game... slow motion happenes at the framerate of the game (30 or 60fps)... there is no drop to make the slow motion effect.