Long ago I wrote a blog post as an introduction with an identical title: https://joelkuiper.eu/semantic-web

At our company we still use Semantic Web (or rather, RDF) for inference and annotation with medical ontologies (UMLS, Gene Ontology, Human Phenotype Ontology, etc). The ease of use of triples + SPARQL (basically a PROLOG-ish unification scheme) is really powerful (and quite performant when using Jena/Fuseki with Lucene as a text index). But it's a far cry from the "dream" of semantic web like federated queries and OpenAnnotations (now just W3C Annotations). Still, every time someone implements an EAV scheme without even considering an RDF triple store I cringe a bit.