It also is very opinionated about dependency management (Conda-only) and is Python-only, where Airflow I think has operators to run arbitrary containers. So Metaflow is a non-starter I think if you don't want to exclusively use Python.
Airflow also ships with built-in scheduler support (Celery?) or can run on K8s. Metaflow doesn't have this. Seems to rely on AWS Batch for production DAG execution.
Airflow ships with a pretty rich UI. Metaflow seems to be anti-UI, and provides a novel Notebook-oriented workflow interaction model.
Metaflow has pretty nice code artifact + params snapshotting functionality which is a core selling point. Airflow is not as supportive of this so it's harder to do reproducibility (I think). This is encapsulated by their "Datastore" model which can locally or in S3 persist flow code, config and data.