Does the caster sense the type of creature it is that was located by this spell? In other words, if the caster senses the location of a single creature, does he or she know it is an Aberration? If there are four creature of these types, but different types, will the caster know what each one is?

Quote from Sorrowmancer >>

Does the caster sense the type of creature it is that was located by this spell? In other words, if the caster senses the location of a single creature, does he or she know it is an Aberration? If there are four creature of these types, but different types, will the caster know what each one is?

It's a little ambiguous, but that's how I've always interpreted it, yeah.

The name of the spell is Detect Evil and Good, but the description of what the spell does is a little vague on the definition Evil and Good. For example, if I had a Celestial that had been corrupted over the last hundred years or so, and was still a Celestial, but his alignment was now Lawful Evil, would this spell detect the evil in him, or just that he is a Celestial?

The description is likely vague on purpose, and is only directly outlining the barebones effects so that it can't be misconstrued. Beyond that, I think it's entirely up to DM discretion what information is revealed with a DE&G cast. In the example you gave, you could describe the presence as "Celestial, but with a sickening, sour aura", or you could say plainly "Celestial, but with an Evil alignment"

Quote from C14GUNNER >>

The name of the spell is Detect Evil and Good, but the description of what the spell does is a little vague on the definition Evil and Good. For example, if I had a Celestial that had been corrupted over the last hundred years or so, and was still a Celestial, but his alignment was now Lawful Evil, would this spell detect the evil in him, or just that he is a Celestial?

The name of the spell is a holdover from earlier editions of the game. The way the spell works has changed significantly, but they've kept the name for nostalgia value. Wizards of the Coast does this all the time (Dispel Magic is another good example).

As a general rule, the spell's description defines what it does and how it works; the name doesn't.