Zotero is awful. It's heavyweight - in fact, a whole separate browser only to manage my bibligraphy (ever tried to use it with ~10k items?). Provides no CLI interface (to automate workflows with scripts). It's data model is weird - e.g., item types include such thing as "instant message", but more academia-relevant types (e.g., "dataset") are absent ("preprint" was incorporated only recently); ISSNs are treated as properties of articles rather than journals. And it boasts it has included its own PDF viewer, whereas I see it as down-side rather than improvement (more bloatware included - why not just follow the division of labor and delegate this functionality to external viewers... ahhh, yes, there is no annotating standard among PDF viewers...).

But all other alternatives for bibliography management I know of are even worse.