The Earthshaker is a premium unit added in the 2.0 Patch. It functions as a buffed up Heavy Artillery, dealing as much damage as an Allied Raider Boom Boom, and is able to hit any ground target at any range. It is exceptionally good at counter-battery fire.
Unfortunately, the Earthshaker costs 60 and also only has 2 ammo, unlike other Artillery units which normally have 3 or 4 shells. The ammo reload time of 6 does help counter this negative. Another major drawback is that this premium artillery unit only has one ability slot, even at Rank 6.
On a positive note, the Earthshaker costs very few resources to repair.