52. can intimidate be used to demoralize an opponent (like in 3e)?
53. with armor class and reflex defense being so similar, do we really need both?
54. can a two-weapon ranger use two-weapon fighting while wielding a two-handed weapon (by say, kicking for the secondary attack)?
55. what notable sacred cows from 3e were slain (i realize this could be a rather long list)?
52. Yes - the enemy needs to be bloodied first, then they are probably hostile, but it IS possible to jack your Intimidate skill bonus up very high and pretty reliably 'take out' one opponent at a time (its more ambiguous if you can force more than one target to surrender with a single action). There are some magic items that bypass the bloodied requirement as well. Of course this sort of optimization generally has some poor favor with DMs... Remember, the DM has ultimate say in what skill is effective in what situation, so you will probably run into situations where the DM will make this harder or even impossible (for example against mindless undead or very motivated/desperate opponents).
53. So far I haven't really seen a convincing writeup of doing without AC. Would armor ADD to your Reflex? That seems odd... I could imagine a game that was less gear-centered and more focused on character ability where armor didn't really do much and was for show, or had other non-defense benefits, but as 4e stands it seems like Ref and AC are both useful concepts. Think of Ref as 3e's 'touch AC'.
54. This is ambiguous. You cannot use a 2-handed weapon with Twin Strike, but EVERY power has its own limits, so there is no definitive blanket rule, all attacks utilize some power and the power always says what weapons etc can be used. Twin Strike specifically requires '2 weapons' and refers to a main and a secondary weapon. You can ALWAYS use Unarmed as a 'weapon', but it is not an off-hand weapon and with a 2-hander you basically have to wield the weapon in both 'hands'. This would generally forbid using a 2-hander and a foot as your two weapons with TS. I think you will find this is the generally understood rule. You COULD use a ONE HANDED weapon and your fist/boot/whatever as the 2nd attack, but the weapon probably should be 'off-hand' since Unarmed is NOT. Some DMs however may let you get away with it (and since Rangers can wield a Bastard Sword in one hand there's not a HUGE amount to be gained with this kind of trick anyway).