The growing interest in the metaverse has led to an abundance of platforms, each with its own unique features and limitations. This paper's objective is two-fold. First, we aim at providing an objective analysis of requirements that need to be fulfilled by metaverse platforms. We survey a broad set of criteria including interoperability, immersiveness, persistence, multimodal and social interaction, scalability, level of openness, configurability, market access, security, and blockchain integration, among others. Second, we review a wide range of existing metaverse platforms, and we critically evaluate their ability to meet the requirements listed. We identify their limitations, which must be addressed to establish fair, trustworthy, and interactive experiences within the metaverse ecosystem. Looking forward, we highlight the need for further research and development in areas such as decentralization, improved security and privacy measures, and the integration of emerging technologies like blockchain and AI, as essential building blocks for a resilient and secure metaverse.