it is defiantly better than phantom hourglass and i thought it was worth the buy (although i haven't been able to finish it because of so many draw backs =( ) i would highly recommend you buy it but if you don't like it don't blame me for buying it XD
If you had already played Phantom Hourglass, it's definitely worth getting! PH was an experiment and ST was the fixed result. It is better in both gameplay and story.