In my opinion, even at four euros, the Director's Cut is barely worth the price if one has already played the game through and through. The vast majority of the game is exactly the same as before, providing the exact same experience. The DC also has bugs that weren't there in the vanilla game. A patch fixed some but not all of them; on my second run, the Social Enhancer's fancy effects weren't appearing when talking to Quinn, and the sound looping bug was still there when exiting the LIMB clinic during the second Hengsha visit.
The game doesn't run too well at max settings on my machine, so I can't tell if there are more changes than what I perceived. There definitely were minor improvements here and there, though. The parked cars, for instance, looked much more pleasant, and some locations were simply better looking. I could not really tell what exactly had been changed in those, just that they were different.
Enemies also have light sheens on them now, which is mostly noticeable during takedowns. It looks alright. An even cooler minor improvement is the blurring of surroundings in dialogues. It works surprisingly well. (Maybe it's the depth of field setting?) Too bad it's not there in the social battles.
I wish they'd done something to the graininess of the skies. On the roof of the Chiron Building, when the devs comment how nice the view is, all I could think of was how shit the sky looked. Maybe it doesn't show if you're sitting on a couch, meters away from your TV. But it totally could be better. F.E.A.R., a game released six years before DX:HR, for instance, has a much nicer night sky (excluding the slight color banding near the horizon).
The Missing Link is now a part of the main game. I was wondering beforehand how the integration would work now that you'd actually have Praxis Points and gear to be removed. With augments, things went like before, except that when leaving the Rifleman Bank Station, you'll get your points total set to the amount you had when entering the pod in Belltower Docks. I think you also get an additional 2500 or so XP after that, which made me max out my augmentations during the final boss fight without power-gaming through the whole game.
Your guns you'll get back with the gifted gear after escaping but their clips are emptied. And that ammo you'll never get back. The only weapon this matters with is probably the Grenade Launcher as there is like 20 ammo or less in total for it. Not that you'd really need the six shots you will potentially lose but still it'd be nice to have kept them. Or at least gained back with the rest of your gear you'll recover when you're done with the place. The gear that you will have hard time fitting back into your inventory, by the way. There's just way too much stuff in DX:HR.
The pre-order DLCs are also there. The double barrel shotgun, silenced sniper rifle, and the explosives are now found in the Sarif Plant, instead of being given in an immersion-breaking screen before. I'm not sure if the 10k extra credits were there, though. All I know is that I always could buy anything I wanted without trouble like before, and that at the end of the game I again had enough credits to buy every vendor clean.
There's also the New Game+ mode now, in which you start with all the augs you acquired during your first run. (All of them, in my case.) I don't really see the point of that; it didn't really change anything for me. But I guess it makes it easier to get some of the achievements, say Pacifist and Foxiest of the Hounds. Just run through the maps cloaked, maybe picking up the weapons and things you want to use on the bosses.
Revamped boss battles
They expanded the three boss battle areas and made it possible to beat them with less combat-oriented builds. Fairly needlessly, I might say. UR-DEDs are now available for anyone; just throw five of them (on the hardest difficulty) at Barret's feet and he dies. And by the time you face Fedorova, you totally should already have the upgraded Typhoon. What augment could possibly be so important to not have three points to spare. Namir dies to five shots from the Grenade Launcher (also available for everyone now) without any hassle. You can still probably exploit the bug and take him down when he's jumping over a wall as well.
I noticed that Fedorova recovers quicker from stuns (or Typhoon's stun duration is now shorter), meaning that you can't chain-Typhoon her like before as she will escape before you'll get the following one off. But it doesn't really change things. Just wait for her to come back and then use your Typhoon again. (The Typhoon cutscene gives you invincibility frames, thus protecting you from her Typhoon.)
The Hyron Project battle remains the silly thing is has always been. Not even remotely challenging, and plenty of time to do whatever you please. Hardly the climactic showdown it maybe should be.
I guess many would've wanted to have non-violent solutions for the boss fights. Or rather, be able to skip them entirely like in Deus Ex. Obviously that wasn't going to happen in the Director's Cut, though.
Developer commentary can be quite interesting. In the case of DX:HR-DC it could've been done better, though. First of all, the implementation could be smoother. I guess they wanted to have some sort of exploration element by not having visual cues where you can find a commentary track in the game world. But at least they could've put something to tell if you have already listened to a particular track.
And some way to resume a track, in case something cuts it off like someone contacting Jensen via the radio. In some cases -- but not all, which makes it frustrating -- the commentary track also gets cut off if the system you're hacking starts tracking you. All you can do then is to go back to the spot and start the track from the beginning.
My second issue with the commentary is how the lead developers doing the commentary are French Canadians (excluding the lead writer) with varying degrees of spoken English skill. Some speak fluent English, with only dropping the first h's from words (like 'Engsha), and others are just painful to listen to, constantly searching for the correct word to use. They could've just spoken French, if you ask me. There are subtitles in the thing after all.
Lastly, the content of the commentary could've been less of lamenting how they wanted to do this and that, and how they had to cut this and that because of time and money. And how they were unhappy with the engine, having trouble getting things like physics to work properly. Apparently it doesn't support dialogues with more than two characters either. That sounded really odd to me.
There is some interesting stuff too, though. Like in The Missing Link, one of the guys points out how players apparently never look up. I do check stuff like grainy skies, but I did miss the ladder at the docks right after you exit the ship. I recall wondering if there was some intended use for the boxes in there but it never occurred me to look up and see the ladder up on the wall. Or maybe I did, but chose not to climb up there and then forgot about it later -- it's been awhile since I played TML for the first time.
Another thing that I found odd was how they intended Narhari Kahn to be a mini-boss battle with the two boxguards in Tai Yong Medical but since you can take him out permanently multiple times before that, they could not do it. But isn't that exactly how it should've been done? Take him down before TYM and you get to skip the fight. That would've been the Deus Ex thing to do.