The reason I'd like to touch on this subject would be that while alphatale definitely has its own merits, improvements could definitely be made. Here's a few I'd like to consider:
Dialogue should fit the character, and excessive profanity should be cut out or more so just reduced for less profane characters (EX: Error404) - this is a very obvious one, and one that is very important. the one thing that Alphatale's dialogue suffers from the most is "Halloween hack Syndrome", overusing strong language on characters who wouldn't seem to be all that profane. If anything, I'd say the strong language would be reserved for something like Infected getting highly agitated. Dialogue should also be dependent on their personality, meaning if someone was, for example, Error404 behaved sociopathically, he would care little about anyone's problems and say something like "Hey, unless It's my problem or if you have anything in return, I'd care less."
Alphatale should definitely be more than just sanses - this is a rather simple one, sanses shouldn't be the only characters, and if there are multiple sanses, it should be done in a way that makes sense. (nyte has me covered on this one) In addition to this, all characters should be given a sort of relevance, be it for one major character's life or another.
More than meets the eye - when developing a character, there should be more to them than what is first seen about them, and should at least have multiple strengths and weaknesses, both power-wise and definitely personality-wise, in order to be established as a concrete character. a personality should always come before the abilities, and character must have concrete motivation behind their actions, and can't just act out of character without being forced to do so. (an example would be Omnipotent sans being cowardly for awhile after dozens of painful cuts from battling infected or dealing with a highly agitated Alpha! chara, not wanting to continue going through agony.)