That's just Yoshiki Nakamura's art style. It gets more a little more refined later on and in her later work. It's still better quality than a lot of manga out there. It's also supposed to emphasize how tall they are. Asago and Tsukasa (boy form) are drawn with more normal proportions for manga, as they are both drastically shorter. Tsukasa gets the similar treatment when she gets all dressed up though, since she actually has a very feminine form.Originally Posted by Death BOO Z
As for the 'gaki' and all the other untranslated parts, they actually fit perfectly in the translation. 'Gaki' and the other untranslated terms are yakuza language. Mainstream Japanese people don't use them often, if at all. By the end of the series, you're so used to the terms you won't even notice. It nicely parallels with how Tsukasa gets more attached to the group.
As Kraco started to point out, this is why I was very specific with the category I laid out. There's a lot more going on than a series of overlapping love triangles. TCP is probably one of the most action oriented shoujo series out there.