Final Fantasy IX on PC worked today. For some reason.
Anyways, let's get to my first impressions!

This game works fine with the DualShock 4 and DS4Windows. The buttons are automatically assigned. Strangely, the O button is for "confirm" while the X button is for "cancel" - it is usually the other way around. Swapping the buttons in the game's options worked for me.
The text font is really boring and generic. The sound effects are strange: they sound somewhat different from the original. I especially noticed this with the sword slash. It doesn't sound nearly as epic as in the original, as if it was cut off for some reason. The German text is unchanged and uses the old German spelling (before the German orthography reform of 1996). Yes, the backgrounds are blurry but it isn't as bad as I thought it would be. The character models look really nice. I discovered new details that I'd miss in the original PS1 game.
What bothers me is that there's an exclamation mark symbol when standing next to NPCs. In the original game an exclamation mark symbol would only appear if there's some sort of secret item to find (or a switch to execute). Every time I stand next to an NPC I don't know whether there's a secret item on the ground or if I'm interacting with the NPC.
The CGI sequences look amazing, the video quality is much better than in the original PS1 release.

Well, that's it for my first impressions.