They screwed with the AI in most enemies to be less aggressive in general, blue essence drops are increased, you can heal at any time so attacks that would have killed you outright in Black and be cheesed out of by spamming healing items, which are a lot easier to get because the BE drops increasing means you have a ton larger window for UTs and thus more money in general to buy supplies. If you're even halfway competent in your ninja gaidening you can break the economy and hit max money very early in the game this way.
Just an example on the enemy thing is that the Berserkers, the most feared enemy in NGB, are total cakewalks in Sigma because they no longer have any strikes that can break your block on first hit. This means that you can just spam counter on them endlessly and take them out without even a modicum of threat.