So I play on a medium-ish laptop, which runs Skyrim with mods at around 24-35 fps. For most games like Metro 2033 and Thief, I get around the same range of fps as well. But then earlier this year I got Sleeping Dogs, which ran at a crazily smooth 40+ fps (for me). And its not like the graphics were compromised or anything. Plus there are thousands of NPCs walking around on the streets, though its not the same interaction as TES games. Still, NPCs. If I remember correctly there were almost no places where I had lag, everything looks nice and smooth even when raining. So its like, why can't more games have performances like that? It was literally the only game which was able to run stellar graphics without lag on my poor laptop.

And then on the other end of the spectrum I recently played some unity games like the Long Dark. And boy, was that horrible. Enabling shadows on that [censored] made me drop to single digit fps in some cases, and around 17-24 in others. And its not like the graphics are stunning. The lighting is fine I guess, but the models and textures are sub par compared to the bigger games. And yet it runs worse? I mean, it just feels ridiculous that a game with crappier graphics actually runs worse. The graphic lag really turned me off for that game.

Edit: The performance between skyrim and sleeping dogs, I know that. But unity really takes the cake.

Because engines are built to take care of different stuff. Assassin's Creed's engine is built specifically to support tons of people rendering at once, along with giant view distance. Skyrim's NPCs aren't "just NPCs" like any others. The engine has to detect everything, their scripts, every piece of their used equipment, magical abilities, etc. so one Skyrim npc will weight down the system much much more than one Assassin's Creed NPC, which is basically an empty animated husk with some minor functions.

Then there's also the fact that, despite them being pros, not all people built fantastic engines with no flaws. Some engines are simply built better than the others. Like how Bethesda keeps upgrading the same old engine instead of finally making a new one.

Skyrim is open world. Too many objects in view at any given time.

Metro has superb atmospheric effects. These are costly.

Sleeping Dogs have narrow streets that would hide majority of the geometry.

It checks out I guess.

PS. I am more impressed with Avalanche's games when it comes to optimization.

You can't really use "Skyrim" and "Optimization" in the same conversation, unless you add "has no" in between.

This right here.

No game engine is good at everything. Unity tries, and you (OP) have seen how that turned out. You can only properly optimize a game engine when it is tailored to the type of game you're making. For example, with a corridor shooter you can pretty much ignore anything that's not happening within a short distance of the player because they can't see it past the walls immediately surrounding them. In open world games like the TES series, you have to render these massive landscapes, and most commonly they tend to use less and less detail for things further from the player. And that's just thinking from a graphical perspective. Throw in physics, AI etc... all these facets have different approaches in each genre.

Which explains Unity. Not only is it intended to be able to make pretty much any kind of game you want, it's also multi-platform. I haven't used it a whole lot so I'm not sure on the specifics, but it's possible that game developers aren't given access to the guts of the engine to make the optimizations they need for their specific game and platform(s). But even if they are, it's no easy task. They didn't code it, so it takes a lot of time and skill to understand its inner workings well enough to make those changes without unintentionally breaking something.

Good question. Maybe you can explain why I can read a short novel during loading screens in Unity games. Bonus question: why did Obsidian decide to create 47261 loading screens per map in Pillars?

I would say, that makes more sense if you compare Skyrim for consoles vs Skyrim for PC.

Some examples are texture down-scaling issues on the Xbox 360 Console, when the game was run from the HDD, crashes, slowdowns and fps issues on the PS3 version when the save files exceeded the 6 MB mark.

(obviously occurred due to extended game play times) and some crashes and slowdowns on the Windows version as well.

However, several patches (official and Unofficial) have addressed a lot of the technical issues and improved overall gameplay a lot.

Fallout 4 will use the same (creation engine) as well, of course modified to meet the expectations of that new game.

Also not to forget, the creation kit. One of the most useful modding tool for creation engine games.

The creation kit has taken advantage of the creation engine's nature and has made Skyrim into one of the most modded games of all time !!!

Good realtime lightning/shadows are among the more demanding things a game can have. Back when I had a rather weak PC, shadows were alwasy the first thing I turned down in the game options to get a better framerate. And with some games I still do, cause I rather play with no shadows than very poorly implented shadows

Definitely one of the rules I live by. First thing, turn down AA. Then Shadows, Draw Distance, tesselation, etc. Of course, the dream is to have a rig that can push all of those to the max and pull 120 fps...

People have already mentioned the reason engines themselves differ, namely that they're designed for different games with different priorities. However, there's another concern: hardware. On consoles, since all hardware will be essentially identical, it's very easy to optimize, and even then they screw it up (Dynasty Warriors slowdown hype). When you have tons of different builds, two major CPU manufacturers, two major video card brands, dozens of manufacturers for motherboards and video cards, and so on and so forth, effective optimization becomes herculean.

Assassin's Creed 1 and its fifty shades of bugs.

Ah, same here. Unfortunately for that unity game there isn't a seperate setting for shadows, sigh. Appears to be only on or off. Maybe i'll have to dig in the config files, though I kinda doubt it. Unity should belong only in browser games! I haven't seen very horrible shadows before though, other than the horribly jagged ones in skyrim.

Some of this might have absolutely nothing to do with the engine, but instead with how it's used. What seems like a small code thing (deleting a reference versus recycling it) or a small art thing (how precise the collision is) can really, really add up. Different games built on the same engine can have totally different problems, because an engine is just a skeleton that needs a whole lot before it becomes a game.

Personally, I think engines are really overemphasized by gamers. If you're talking about stuff like Unreal or Unity, there are totally different games built on them, and unless you're told you'd probably never guess. If you're talking about an engine tailor made for a game, it becomes impossible to compare it to a jack of all trades engine.