Persona 4's Social Link system is one of the elements that has changed the least since Persona 3. I have already discussed both Persona 3's version of Social Links and a few ideas on how to change that system, and unfortunately many of the issues I raised earlier are just as problematic, if not even worse, in Persona 4. As long as the Persona games still use the classic Shin Megami Tensei system of acquiring new "monsters" and fusing them to create ever stronger "monsters" (which is its own issue), then the gameplay benefits of building up Social Links will be perfect as-is, but the actual process of building up those Social Links is still significantly flawed.
The greatest problem of the Social Link system is still the lack of presence and development of the Social Link characters. Most of the Social Link characters are still just random people that are completely unrelated to the main story of the game, so you really only interact with them in the ten scenes that build up the Social Link. Many still don't show up at all other than the times in which you can hang out with them, and none of them react at all to the main plot of the game. At the very least, the game designers could have given these characters the same constant presence that many of the nameless recurring NPCs in the game have. After all, every last person walking around the game world (other than a few who only show up for quests) has their own personality, quirks, problems, and reactions to the events of the game. there is no reason the game designers couldn't have given the same kind of dialog that the nameless NPCs use to convey so much to the player, in addition to normal Social Link development. Even such a minor addition could have added a lot. As it stands, it often seems like the Social Link plots and the main story of the game are so separate they may as well not take place in the same setting or involve the same main character.
Another great problem is the nature of the Social Link subplots. In almost every case, these subplots involve some problem that the Social Link character is facing, and how this problem gets solved. Often, this problem takes the forefront to the detriment of actual development of the character or portraying a believable friendship with the main character. This is actually a pretty major problem from Persona 3, but it has become more apparent to me since I last discussed this issue. A good example of how bad this can get is seen with the Social Link character Yumi, a girl the main character can meet if he joins the Drama Club. The first few scenes in this Link, which focus on introducing Yumi's love of acting and straightforward, strong-willed personality, are quite fun, but shortly afterwards the entire thing gets hijacked by a plot involving Yumi's estranged father falling ill. Almost the rest of the Social Link subplot is a long chain of scenes at the hospital in which Yumi laments her bad luck in life. These scenes don't even really portray how the hero helps her through this (that is just left as a vague implication), instead, they simply focus upon various stages of how Yumi's problem develops, almost completely ignoring the main hero's presence (and thus the player's importance). Even the idea that this is supposed to be the drama club Social Link is ignored by this subplot, which makes most of the fun parts of the first few scenes involving Yumi completely meaningless, and really stretches the question of why you can only see scenes involving Yumi in the hospital on days when the drama club meets. I am certain that the writers for the game intended this to be a fairly emotional story, but in creating a story about how Yumi deals with her problems with her sick father they completely forgot to actually tell a story about a growing bond between Yumi and the main character, which is what it should have been. This kind of focus on a character's problems, rather than on the character itself and how that character interacts with the main character, is far too typical for Social Links.
With all of that said, Persona 4 has indeed made a few significant improvements over Persona 3's version of the Social Link system. The two biggest are the addition of every Persona-using ally as a Social Link (which addresses a major problem I had with Persona 3), and the change to girls' Social Links so you don't automatically pursue a romantic relationship with every girl you know. The former change is probably worth its own post, so I'll get into it another day. The latter change is simply a much-appreciated improvement, since it means that you don't need to act like a two-timing skirt-chaser in order to build up every Social Link, and can feel more free to build up a girl's Social Link even if you don't want her to be the main character's girlfriend. Actually, considering some of the important secondary effects of building an ally's Social Link and the fact that many of the ally characters are girls, the latter change is practically essential to Persona 4. In addition to those two major changes, the added stronger link between Social Links and the hero's attributes, so raising Social Links both more frequently requires built up attributes and raising some Social Links will also improve certain attributes, also is a nice general improvement, and the pay you earn for Social Links involved with part-time jobs is another much-appreciated addition.
This is such a big part of the game that I still have quite a bit more to say, particularly about individual Social Links, but I should probably save it for another day. This post is getting long enough.