I've mentioned this before somewhere on the forum, but I like season 4 because it feels out of place. I personally think that's the point. They are no longer in high school, and a lot of people feel adrift once they enter college and adulthood.
Parker is a manipulator who pretends to be a nice guy to sleep with women. This is entirely realistic, and an experience a lot of people have dealt with in their lives. After Buffy spent nearly three years in an on again, off again relationship with Angel, it makes sense that she would delve headlong into something with Parker. After all, there were a lot of things Angel and her could never do, so I think she longed for a more normal relationship. It's just sad that he used her. And I saw a comment where someone said they hated how Buffy asked if she had done anything wrong. Again, realistic. Many people feel that way once they realize the other person isn't interested in having a relationship, and sex is involved.
Personally, I always liked Riley as a love interest for Buffy. He's more down to Earth, but he's still fairly strong and can mostly keep up with Buffy because of it. There is a hint of mystery still involved due to the whole military aspect, at least in the beginning. He even turned his back on the military because he fell in love with Buffy, and because Professor Walsh tried to have her killed. He's turning his back on everything he thought he knew.
Willow and Oz break up, and literally after that, Oz's entire plot is him leaving so he can try and control his werewolf powers. Willow moves on, delves deeper into magic, and ends up falling in love with Tara.
Without his job at the school since it literally blew up, Giles is just kind of there. He's no longer a Watcher, and his apartment kind of becomes a hub for the Scoobies. He feels like Buffy no longer needs him and considers returning to England.
Xander hops around from one job to the next and has a very strange relationship with Anya that I would also say is off again, on again. He's not sure where he fits in and is definitely trying to find himself.
Spike gets implanted with the chip and can't get up to his usual schemes because of it, so in turn, he ends up fighting alongside the Scooby Gang at times, then helps Adam in hopes he can get the chip out.
Basically, the entire season is about the awkwardness of adulthood and trying to find your own path in the world, which I think season 4 does exceptionally well because it often feels disjointed and out of place. This comes to a head near the end of the season when we see the group get into a huge argument - that quite frankly doesn't make much sense - but I think that's also the point. They have all changed, and so the group isn't the same either.
While people dislike The Initiative plot and Adam, I personally think the involvement of the government with supernatural forces makes a lot of sense. After all, the government always meddles in stuff. Unfortunately, I think the idea was just executed poorly. I feel like some of that likely has to do with budget, and if a similar idea was rehashed in a reboot, it might be done better.