Watch Dogs: Legion is about as good as you'd come to expect from this series. It's not a bad game however, it is just really lazy and underdeveloped.
Gameplay wise, it is very much identical to Watch Dogs 2 however it implements new features such as multiple playable characters (known as operatives) and these characters will have their own routines that they will live out (or so it feels like at first glance). To recruit an operative, you can just go up and talk to them (help them with a problem or liberate a borough if they don't like DedSec) and they will give you a mission - usually go and collect an Ambulance or protect them from an assassination attempt. They will then return the favour and join your cause. Beforehand, you can check these operatives skills and abilities (for example hitmen can carry lethal weapons and are generally more maneuverable in combat, and doctors and police officers can give you access to restricted areas) However, once you upgrade your skills from the main menu, you will only need to use certain operatives throughout most of your playthrough. Making this mechanic interesting, but underdeveloped.
The game's main setting is London, the cultural capital of the world - home to many different walks of life. Which has unfortunately come to disarray after a planned terrorist attack occurs and is blamed on DedSec (the main protagonist faction of the Watch Dogs series), and the group soon disbands. It is up to you, and your operatives that you recruit and play as, to conquer London from Albion - a private, corrupt military group run by Nigel Cass (who soughts to bring down DedSec) and find out who set up DedSec for the terrorist attacks.
Just to mention in this review, the voice acting in Watch Dogs: Legion is on par with Bethesda games such as Oblivion and Fallout 3. And it feels that there are even less varieties of voice actors than in those games - most of my operatives speak with an Irish accent, and there's another large group that speak in Jamaican accents. Not to mention the dialects sound too over-exaggerated for a proud member of the British Isles, such as myself.
Additionally, the music in this game is nothing really to mention - it's primarily made up of UK Grime / Rap and Punk Rock. Again, not much in terms of variety.
If you ask me, I'd recommend this game only to people who are interested in the Watch Dogs series, sandbox games, open world environments. The recommended value of this game is around £20 - £25.