As a vocal fan of the series, I'd say that World is sitting right below the original in terms of best content. The unlocks are paced very well, and the purpose of challenges is satisfying, as they net you more diamonds. I'm not too keen on aesthetic changes myself so I stray from the costume or hades and focus more on the gameplay. While I am disappointed that the goodbye mechanics are gimped compared to the previous installments of the game I understand Nintendo wants to screw people out of their money and obtaining evolutions from goodbyes would defeat the purpose.
I am very excited to start obtaining rusted figures and Mega Stones, and I think the game has done a great job in making those feel like late but crucial changes. Is the title worth 30 bucks? I don't think so, maybe 15, but it is nice that there's a fund cap for any poor souls that invest that much money.