It’s not that hard for me, when I take time to say each syllable one at a time: Wor-cess-ter-sure.
But if it unexpectedly appears in something I’m reading, then it could be a challenge.
I think it might be because it’s significantly longer than a lot of more familiar city names, e.g., Boston, Paris, Rome, London, Houston, Dallas, New York, Chicago, etc.
Because it’s the name of a relatively obscure city, and not among more frequently encountered lengthy words such as nouns and verbs, it’ll be harder pronounce, unless one is familiar with urban MA. Actually, I think at least some Mass. residents pronounce it “Woosta”.