Here is the full list of all 40 Destroy All Humans! achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Set something on fire, then use it to destroy a hapless human
Demonstrate Furon free spirit near a warning sign placed by the human authorities
Display Furonic aeronautic prowess by soaring through giant human pastry without soiling your feet
Abduct and drain a vehicle to replenish your saucer's shields
Ace all challenges!
Complete all optional mission objectives! (Use the Holopoxdeck if you have to.)
Re-visit a mission in the mothership archive's Holopoxdeck
Destroy humanity's last hope and initiate the subjugation of the species
Destroy the pathetic human attempt at a robot overlord
Destroy a certain irritating simian warlord once and for all
Invade Capitol City
Invade Union Town
Ace a Race challenge with a three-star rating
Obtain at least a two-star rating for each challenge type
Ace an Armageddon challenge with a three-star rating
Invade Area 42
Evade a rocket by dashing
Explore the more offbeat parts of the mothership
Use your saucer's Repulse-O-Tron to fend off homing missiles
Upgrade your saucer at Pox's Lab in the mothership
Transmogrify an object to replenish your ammunition
Try out a new look for Crypto in the mothership's archives
Fully upgrade one of the branches of a weapon or ability
Invade Santa Modesta
Ace a Rampage challenge with a three-star rating
Throw a human into the air and juggle them
Accelerate Brain Extract or Transmog by mashing that button like you mean it
Use PK to destroy a human with another human
Upgrade Crypto at Pox's Lab in the mothership
Destroy multiple humans with a human-made explosive
Abduct a cow with your saucer
Throw something into something else with the saucer's Abducto Beam
Stay covert by scanning primitive human thoughts
Invade Rockwell
Recover a Furon Probe
Ace an Abduction challenge with a three-star rating
Revisit a missionless invasion site and complete a challenge there
Consume a human brain to kickstart your shield regeneration
Destroy a human with a weapon and another with a psi ability at the same time
Invade Turnipseed Farm