The plant itself doesn't look too bad, though the stem & branches are very thick, the leaves thick, & the whole thing goes curly at the top, but the tomatoes (of which there are far fewer than on the other plants) are disastrously bad.
Plant
Tomatoes
They're all going like that as they grow. Only one plant affected, luckily: the tomatoes on the others are plentiful & looking perfectly normal.
Is it a disease? A nutrient problem? Something I can do something about? Or should I just give up on this plant & scrap it?