TiDB is interesting, but missing more features from MySQL than CRDB is missing from PostgreSQL, so it's effective if you want sharding on mysql but will need a few more releases before it gets polished. Vitess and Citus are good options if you just want sharding on top of existing mysql or postgres with full query support within a shard. There's also Yugabyte which is multi-modal Redis/Cassandra/SQL offering with multi-regional capabilities.
CRDB is a great product with some of the easiest operations (although key management is a nightmare that they do not have a good plan for). It's fast enough for point-lookups and makes it easy to distribute and replicate your data across zones and regions. All nodes are part of a single cluster so read and write latencies will be high for global deployment, with the enterprise version having a workaround for local regional reads using pinned covering indexes. That works, but further lowers write performance.
It also has trouble with large transactions and the middle ground between OLTP and OLAP with heavy joins. Good choice if you need easy scalability and SQL interface over performance and complex queries.
The gap of features missing is documented here:
I would rate compatibility as actually pretty good: all but one SQL mode is supported (which is a feat in itself), and most of the SQL functions are supported.
There are some exceptions though, some which are addressable (missing functions) and some that are not (often a property of being an optimistic system).
We try to be as transparent as possible on this, which might be part of the reason why you feel there is a lot missing?
If you have specific examples, I would be happy to clarify. We also have a course designed for MySQL DBAs, which is designed to make the adoption easier: https://www.pingcap.com/tidb-academy
Views and CTEs are probably the biggest missing pieces now.
Window functions & CTEs are only very recent features in MySQL 8.0 (TiDB is 5.7 compatible). None the less, they are important for HTAP workloads, and I'm looking forward to seeing them too.