RetroGaming

From my understanding, these don't have any additional content that the other releases. Any additional dungeons, bosses, equipment, or story will not be found in the Pixel Remasters. It's the original game.

However, there are quality of life additions like maps, save spots, auto-fight, "fight next enemy when it dies", and translation and bug fixes.

For the record, I only beat FF1 on Pixel Remaster, the 3D FF3, and the now-defunct previous re-release of FF5.

The biggest change is the visual redesign, which uses a brighter color palette and slightly more blended sprite designs to approximate how the original games would have looked on a CRT (along with miscellaneous small changes, such as a FF6 party member being redone to look closer to the concept art). They also all have new, optional soundtracks. Most notable is FF3, which is a full update of the Famicom version and doesn't have any similar releases. The old DS 3D remake had different characters and a light story too, so the FF3 Pixel Remaster also has a completely new script for Western audiences.

I'll emphasize what was brought up already--none of these have any content added in the various ports over the years. Extra dungeons, job classes, FF4's late-game party change, all that isn't here.

I've spent some time with the first three, so I can give my opinion on those.

The FF1 remake is very different experience than the NES original. That version had a ton of minor bugs that gave that gave it a unique balance. Every subsequent remake, including the pixel remaster, has been an attempt to fix those bugs, and add modem QoL features, and then rebalance the game to try to keep the same feel. I think the pixel remaster is a good game, and comes closer to the feel of the original than some other remakes, but it is still a distinctly different experience. I'd characterize it as a different game wearing the same clothes.

The FF2 remaster, on the other hand, is probably the best way to experience that game. The Famicom original is notoriously unbalanced and player-hostile, but those problems are effectively bypassed by the simple inclusion of two QoL features: a map, and a one-button autobattle. It took decades, but FF2 is finally worth recommending to more than hardcore fans.

The FF3 remaster is in an odd situation, in that this is the first time a close approximation of the Famicom original is officially available outside of Japan. The DS remake from 2006 is a significantly different game, especially in the first couple of hours. I didn't play as much of this one as the other two, but I can't imagine it deviates too much in the later parts of the game. I would guess, though, that the more flexible save mechanics make the notoriously difficult final three dungeons much more manageable, though maybe more prone to soft-locking.