You're not the only person who doesn't like the series, in much the same way that not everyone likes Harry Potter, despite its success. They just aren't for everyone. We all look for something different when we read and for some people the Hunger Games is too linear or, in your case, Katniss isn't very likable. Personally, I don't believe the main character has to be likeable for it to be a good book. Katniss is the vessel for the story because she is central to the plot line, but it doesn't mean she is going to be the hero we all want her to be; that's just who she is. And I would argue that she does grow over the course of the trilogy but that growth is subtle and it still doesn't necessarily result in her being a likable character, it just means she changed. And, as for her being by herself, I felt that it helped convey that sense of isolation that she felt and the blind injustice of the games (because we couldn't see what everyone in the capitol was thinking). It's a common practice to lock the reader in the main character's perspective to the exclusion of things going on in the greater world. It helps to keep the story on a set path and give the perspective of just one person.
But, I'm not saying all of this to suggest you are wrong with your opinion, I'm saying it because it's MY opinion. I don't believe the book's success was based only on its marketing because readers have to actually like it for it's success to spread beyond one book or spread by word of mouth. Not that all popular books are well written, but they do contain something special that is hooking so many readers. For me the Hunger Games was a chilling portrayal of how sickening humanity can be. While these games in particular are fictional, watching people and children fight to the death, isn't; it's historical. We see the dangers of repeating past mistakes and power corrupting the elite. We see a character who, while just trying to save her own life, sets off a chain reaction that she can't understand or control, only to then meet the people who would use her for their own gain. I liked the Hunger Games because it surprised me, horrified me, and ended on a note that was different than most generic happy endings.