it's a combination of euphoria, a slight mania, boost in enthusiasm and motivation, and it quite possibly 'unlocks' part of your personality (i.e. the funny part, since it completely eliminates your inhibitions to tell racy jokes).

so just like you said, this is why it's so hard for problem drinkers to cut down. it's just a whole different experience than a person who has a couple and then feels dizzy and wants to sit down.