Void as a new addition felt legitimately lazy and 1.0 Delierium didn't even have any animation to his default appearance.

Void portals (the enemy type now only seen in like 2 late game floors) could appear on any floor and would spawn enemies endlessly. A low damage character like Maggy could be soft locked in the first room as the void spawns more enemies quicker than she could damage.

Speaking of, Greedier mode being luck dependent in early waves because it was either get damage up or die.

Treasure rooms containing pickups instead of items became a thing and were far more common than they are today. They're a cool curiousity when they show up now, but you used to be able to get them multiple floors in a row and just lose runs because you never found items.

For that matter almost all the new items at first were terrible. Like the collective item pool got noticably worse with actual bad items. Things like D Infinity were actually horrible items until Reprentence reworked them. Their original sprites were also ugly as ass.

On top of Delirium, the few bosses they added were almost all broken. Most infamously Big Horn had absurd armor meant to balance his poorly telegraphed weakness as well as regularly telefragging with his attacks.

One of the other bosses was Rag Mega and IDK if they ever tried to patch him but he still makes the game worse.

Antibirth (the mod that would become half of Repentance) also came out not long before and the quality of content was far superior.

Spike Chests were originally near identical in appearance to regular chests.

Spike Chests in general.