I'm a Scot in Scotland, and I own the dress. I like it a lot. It's cool to wear - as in not hot - but doesn't expose my upper arms which I don't like having on show. I can't imagine wearing it into autumn, to me it's a bare leg dress, but I've had good cost-per-wear from it, and it's washed really well (it's viscose, not polyester). I'm 5ft 6, size 10, and while it's not the most flattering thing I've ever worn, I think it looks nice and have actually had women stop me and say it looks good.
Honestly, I see LOADS of things I hate in the shops, I just walk on by. I think the fact this dress is so popular and the media's got a hold of it means people feel they have to have an opinion on it, whereas in reality most people probably see tons of things they perceive as ugly every single day, but don't bother saying it out loud. The sneery tone of that Instagram account is horrible, but actually some good has come of it - they're co-hosting an event which will benefit a period poverty charity. The pieces in the media have, I think, generally been positive.