I preordered the PC version of the game when it became available and I've been playing it since the 24th.
I have a 4K GPU and monitor and as you expect, the visuals are beautiful.

It was a rocky start playing it the first day. After nearly 8 hours playing the game, It crashed 26 times and the last three crashes caused a system reboot each time. I was worried it corrupted Windows somehow but it didn't.

My first complete run through I noticed how quite the various mission were from the marines and grunts. There is very little combat dialogue from the marines and grunts. I wonder if a large portion of the marine and grunt combat dialogue was removed so they wouldn't have to pay the voice actors royalties? All of the original combat dialogue should be restored in the game because the encounters are too quiet and you lose the immersion and sense of combat. The Elites have only a handful of combat dialogue lines as well.

The game plays more of less like the original did. I found all the skulls and terminals and completed all difficulties in the first three days, I have three achievements left to get and I will probably ignore the LASO achievement unless I feel adventurous. The Assault of the Control Room is my favorite mission in the original game, but in Campaign Evolved, it's my least favorite. I'm not fond of the redesign of the interior areas and it seems to be a much smaller map. I noticed when you get to the bottom on the snow field that there are far fewer enemies then the original game. I do like the redesigned Library mission, but most of Guilty Spark's normal dialogue has been cut as well.

I really don't like the weapons sounds at all, they sound, for lack of a better description, rather glassy. Maybe in a future update they should add a new skull that restores the original weapons audio and all of the original combat dialogue.

I'm very disappointed with the new Needler. The Needler is my favorite weapon in the original game. I would like to see the Needler restored to its original characteristics. I left out the Bonus Missions for now until I play them on harder difficulties.

I like playing the new game. It does have some bugs and glitches that I hope will be addressed in future updates.