Check you have not accidentally engaged Silent or Theater modes. Then look in the Watch app on your iPhone, and have a play in the My Watch/Sounds & Haptics settings. If you change the Haptics setting you should get at least a tap on your wrist. If you don’t get this try a forced reset (press and hold both buttons until the Apple logo appears, then release and let the watch reboot).
If still not working you could try unpairing then re-pair the watch. Try restoring the backup made during unpairing for the first attempt, and you have the fallback of trying again but setup as a new watch with factory default settings for a second attempt.
If even a re-pair doesn’t get it working the Haptic Engine in the watch might be defective, Contact Apple Support To arrange getting it checked and serviced.