I don't have DC. And IMO DX:HR the release version was already a masterpiece. Yea, boss fights were retarded, but do I look like a person who cares for boss fights when the rest of the game is unbelievably good?
Should I buy DC and replay it?
I grabbed the director's cut from some sale with 5 euros and I think its not the worst way one can spend 5 €
Main feautures:
The Missing Link DLC is now fully integrated into the base game. I think this was the main selling point for me. It really makes sense and it was obviously meant to be part of main campaign. I recall they weren't able to finish the level when main game was shipped, so it was cut, but later released as a standalone dlc which was worth of every euro I paid. Now it is finally integrated into main game.
Other two dlcs (Tactical Enhancement Pack and Explosive mission pack) have been also integrated to the game in more immersive way. Explosive Mission Pack content includes the tracer tong rescue mission.
In the orginal dx:hr tactical enhancement pack dlc basicly spawned two new weapons into your inventory in the hostage rescue mission. Now the game doesn't do that anymore. Those weapons (silenced sniper rifle and double barred shotgun) are placed in the hostage rescue mission location which makes much more sense to me.
New game+ mode: Option to start New Game where previously selected augmentations will carry over. Weapons from the previous playthrough will be gone though.
So when you have completed the director's cut, this new game+ option becomes available. Adam starts as almost fully augmented and it will certainly offer a different kind of experience. I just replayed the first detroit mission and it was kind of fun having the clock and other cool augs right from the begining.
45 Minute "Making Of" video and Around 8 hours of commentary from Eidos Montreal. I have not yet experienced these, so I can't comment them. What I've gathered is that people seem to like the commentary, but I lack first hand experience.
Redesigned boss fights. I'm with you there, the problematic nature of boss fights in the orginal dx:hr was somewhat exaggerated, but they did kind of stood out because rest of the game was so great. Still I never had any problems with them.
That being said atleast there are now alternative ways to take out bosses if player so desires. Don't just expect ground breaking changes. They more or less play the same, but for instance with Barret there is an option to reprogram some turrets and the room design is slightly different.
Improved textures. Deus Ex: Human Revolution Director's Cut vs The Original Version (PC Graphics Comparison) [HD]:
https://www.youtube.com/watch?v=VGB27zgAcDU
As you can see, there is a slight difference in quality, but imo orginal DX:hr was a gorgeous game on it's own.
Lastly there is a small change how augmentation power renegerates.
By default Jensen will be able to regenerate two energy cells on all but the hardest difficulty.
This change had no effect on my playthrough since I played with "give me deus ex" -difficulty setting