it's not the same drug.
the brand name estradiol attaches the active estrogen agent to a salt that gets metabolized by your liver, which results in stable levels of estrogen that get released through your endocrine system. this is the most natural way to do this, which isn't necessarily the best, but the stability ensures that the mood swings are kept to a minimum.
the generic estradiol encases the active estrogen agent to a water molecule that is meant to enter your blood stream directly (and should probably be taken on your tongue rather than swallowed), which produces immediate spikes and sharp trails. this is more akin to popping estrogen as a drug. while it will lead to mood swings, the feminizing effects will be less effective.
if they were the same thing, i'd take the generic. but, i actually think that the hemihydrate forms of this should be banned, along with injections.