I liked Devastation a lot but I think Fall of Cybertron is my favourite Transformers game. As well as weighty shooting mechanics it is mechanically varied and tells a surprisingly enjoyable story. Taking in both Decepticons and Autobots while maintaining the Transformers dichotomy of knockabout fun/ portentous nonsense.
It also looks great and has a fantastic sense of scale required when you have robots who are also literal cities.
Mad props as well to the PS2 game Transformers. An under appreciated gem in its time. No idea how well it will hold up now. When I have space to set my PS2 up it will be one of my first discs in the machine.