Season 1 was good.
Season 2 was just terrible, and would be better if I just skipped it. Only last few episodes in season 2 are interesting. the rest is a mess of random events.
Season 3, however, is probably the best. I just love the witch cult. Probably the most awesome evil people in anime ever. I feel like more thought was put into making villains than making heroes in Re:Zero. Lets face it, if it wasnt for witch cult, anime would be way more boring as season 2 shows, where witch cult wasnt much present. the reason season 3 is better than season 2 is simple, because witch cult is much more present in season 3.
Main hero is some insane supportive character who obviously forces himself to be supportive of others when he clearly doesnt mean it and his compliments are always exaggerated to the point where it looks like sarcasm.