Having had the "pleasure" of playing this for a bit recently I noticed a few things. Besides the art and sound fuckups which are well documented, there are also some gameplay changes. Now, if you haven't played DeS for a while, they might fly under the radar, but I had finished it just a couple of days before on the emulator so they stood out.
In the tutorial, I had a harder time parrying the knights compared to the original in which I don't have any issues doing it. The timing of their attacks seems to be slightly different than the original and all the added details on them makes their move much less clear than in the og. Vanguard also has somewhat different hitboxes. The standard tactic of staying behind him still works, but I died a couple of times which, again, is not something I have an issue with the original game.
In 1-1, the little blobs on the Phalanx fall off much faster and in 1-2, it seemed to me that the Tower Knight is much more precise with his long range attack that he does when you're on the walls.
In 4-1, it's easier to dodge the roll of the skellies since they don't smash straight into you as they used to do all the time and would stop just slightly short of impact. They can still hit you with the roll, it just takes a lot less effort to avoid it.
In 2-2, something seemed off about Flamelurker, but I can't put my finger on what exactly was changed. It might be just that the new model and graphic effects are not as clean and crispy as in the original making it harder to understand what is going on. And in 2-3, the Dragon God got fucked up. Every time I replayed DeS all I did in this fight was just run, smash the pillars, maybe eat a punch on the way, shoot the ballista, repeat for the 2nd one, win. In the remake, this seems impossible to do as the thief ring has very little effect and the Dragon God is much more aggressive with his punches.
And they also removed the dupe trick without adjusting the upgrade mats required. One of the things DeS did poorly was the upgrade system and the insane amount of mats needed to get the weapon to max level to the point I consider duping them a legitimate mechanic. This is one thing they really could and should have rebalanced, but they didn't so have fun farming. Wonder if Pure Bladestone still drops only once every 2000 thousand years on a full moon and if Mercury is aligned with Uranus.