But surely that's the trick, right? Beating Mom is a challenge for a complete newbie, but after you've got a few hours (or tens) under your belt, any half-decent set of items should be enough. Mom's heart should be tougher and what lies beyond, well... Having a 'Dark' chest alternative, plus completely re-worked final fights (Heart, Isaac, BB, Satan... ???) and hell, the inclusion of a Hard mode on top, I wouldn't worry about the game being too simple just yet.
Also, BoI has always taken the approach of 'fuck balance'. If you get Brimstone, Monstro's Lung and Tammy's head then you've basically won, if you get Lemon mishap and a broken teleport then go fuck yourself, feel free to roll again. The huge number of new synergies are the main thing concerning me in that there might be a few too many ways to become totally overpowered, but I'm nowhere near far enough in to determine if that's the case yet.
EDIT: Some things have definitely been tweaked to be easier, e.g. horsemen do charge more slowly and Mom seems to stomp a whole lot less, maybe these are the kind of things tweaked on hard mode? Haven't tried it yet.