The TaylorMade M4 driver is generally reviewed as a forgiving driver that prioritizes straight distance and a solid feel, though it may not suit every player's swing and can have higher spin rates. Key technologies include Twist Face, Hammerhead slot, and Geocoustic engineering, which are designed to improve off-center hits and ball speed, and contribute to a powerful sound and feel. Overall, it's considered a strong performing driver for most golfers, especially those using older drivers, with many praising its forgiveness and solid feel. 
Performance and technology
Straight distance: The M4 driver is designed to deliver straight distance through technologies like Twist Face, which counteracts side spin, and the Hammerhead slot, which helps maintain ball speed on low-face strikes.
Forgiveness: It is highlighted as being particularly forgiving on off-center hits, with many golfers reporting consistent ball speeds and straighter ball flights.
Geocoustic engineering: This technology combines geometry and acoustics to improve forgiveness and sound.
Feel and sound: The M4 driver is noted for a solid, powerful feel and a distinct "crack" sound off the face, particularly due to the Geocoustic sole and Hammerhead slot. 
Who it's for
The M4 is a strong option for mid-to-high handicappers who prioritize forgiveness and accuracy.
Golfers with older drivers (3-4 years or older) may see significant improvement in their game with the M4.
Players who are confident in their ability to find the sweet spot may prefer drivers with more adjustability, like the M3. 
Potential drawbacks
Some reviewers noted that the M4 driver can produce high spin rates, especially with certain shaft combinations, which may lead to shorter carry distances for some players.
While the Twist Face technology is beneficial, its effectiveness is dependent on the individual golfer's swing and delivery.