Here is the full list of all 35 Dead Island Riptide achievements. It takes around 40-50 hours to unlock all of the achievements on Windows.
Gain level 70
Finish all quests in the game
Find and kill all named champion monsters located in dead zones
Kill 100 zombies using boat speed boost
Find all the secret files of Consortium
Find all collectibles
Mark 100 opponents which then were killed by your coop partners
Find all voice recordings of a journalist
Find all pages from the guide book
Kill 100 zombies with thrown melee weapons
Finish quests for Cecil in hospital
Kill 100 enemies using charge attacks
Kill the Twins
Kill 10 zombies with one mine
Finish quests for Dr Kessler
Find 50% of collectibles
Kill 25 zombies with a chainsaw
Gain level 50
Finish the game
Complete all the main quests cooperatively with any number of partners
Deafeat Harlow
Enter the docks in Quarantine Zone
Kill special enemies: Grenadier, Thug, Wrestler, Infected, Suicider, Screamer, Butcher, Floater.
Make pact with Serpo
Survive the horde on the roof
Rescue 20 NPCs from clench
Kill 100 zombies with a kick.
Gain access to a long range radio station
Clear out the cinema
Reach Henderson
Successfuly defend the tunnels entrance
Install 5 barricades in any hub
Kill 50 zombies by smashing, decapitating or shooting them in the head
Find a boat to travel through the jungle
Escape from the ship