Guess I'll start out Hardcore, I only wish the recipes weren't so tedious (yes, they are not "hardcore", but tedious). Going to finish Digital Miner (found a Nether Iridium ) and kill Wither (already have 3 skulls) somewhere later on my SC world, sucks that I have only 10 Pinky meat for Burritos.
Also please balance Spriggans, Ghosts and Chupacabras. Spriggans are shooting too fast (one beam kills you, and they're unkillable in early stages of the game, as they fly up on hit), Ghosts using their fear with too little delay and Chupacabras are moving way, way too fast making them OP (charging you in and out, you're mostly unable to hit them due to their speed).
I think that pushing "difficulty" through "nerfing" recipes is rather lazy approach to making a pack actually hard. What would make it harder is implementing HQM, through which you can not only push challenging/rewarding goals (incentivising exploration (would require small nerf to Infernal mobs), making full-out-underground-pussy-mode not the only option ), but also give players a goal (as for now it's rather "fucking around", "for what am I doing this"). With HQM you can make/propose players to explore everything, if not most of what the pack offers/developers are trying to achieve with the pack.
Only other issue I see is that the version on the launcher is listed as 1.5.1. I know you just uploaded 1.5.5, and I'm not sure if that is because FTB hasn't updated. In the modpack folder the readme version is 1.5.1 as well.