My main gripe about the IGAvanias is how most of the difficulty in these games is a matter of self-restriction as a result of overpowered shit being thrown in with absolutely no regard for balance, like the rainbow shield in SotN which kills everything practically instantly. Then you get cool shit like Richter Mode with his fighting-game like inputs, but you're still left with crappy ass bland stage design. SotN is only really fun with challenge runs, but the game should be encouraging that from the outset instead of throwing a bunch of random shit at the player to see what sticks. It's the same problem with games like Dishonored.
CotM also had the right idea with its class system where the name you would input would determine your class and your card set, on top of other things like weapons. It being locked behind name inputs is retarded, though nowadays we have the internet for that. IGAvanias as a whole would improve thousandfold if unique playstyle-altering abilities would be tied to pre-selectable classes rather than grinding souls.