To sum this game up briefly, it's short but sweet.
Kill infected humans & boss zombies on infection ruled islands using bodily combat moves, throwables like grenades, bombs, a Molotov or two and different grades of handheld weapons (you can even make your own).
The game's plot is based around a group of survivors -some immune to the virus, some just lucky to not have been bitten- who live just long enough to be taken by the government for "testing". After waking to discover the army gone and the scientists' victims of the virus themselves they are left to their own defences:
Riptide is very much built for its online co-op mode. When confronting a horde or the super tough boss zombies having more players helps a lot. However you can only play with others once you've finished the prologue alone, which, if you're not used to the original game can take a while. Once you're done escaping from the zombie infested ship, the characters end up on the gorgeous tropical island of Palanai. Here players will meet, greet & trade items with other characters.
Killing zombies isn't all you do (if it was it'd probably be a lot easier); as your fellow immune & lucky survivors are constantly sending you on quests to find things they're too lazy or scared to themselves. The difficulty and rewards of quests are varied and usually affected by a character's skill level. They do get maddening though, and I must admit to giving up on a few after hours spent running in circles, trying to find the big screen location of the little red flag on the map.
On the other hand, quests can give you more drive; after all players don't get many cool weapons, extra XP or added combat abilities without completing most of them.
Now back to the ass-kicking part. The designers of Riptide really know how to make killing zombies extra entertaining, this can be done in many ways:
Kicks or punches - to the head does the most damage, but if you go for the undead's legs it slows them down a lot.
Cars - great fun. Cruising around the gorgeous island, accelerating through zombies as you go. Sometimes essential to avoid walking for hours, driving cars is more of a novelty since it takes away the difficulty of combat.
Boats - The only way to travel for some parts of the game. Not very user-friendly, not very fun; especially when zombies you've missed hitting with your boat climb up and drag you into horde filled waters. Oh, and the mini map doesn't work so well here - you will get lost. Lots.
Throwable weapons (grenades, Molotov cocktails & knives) - handy for super hordes but can be easy to misfire (doorways and ceilings can cause many to rebound onto characters).
Handheld (melee) weapons - easy to find all over the islands, they each require certain skill levels to use them, the game's ample range lets you use almost anything from hat stands to wrenches and claws. My preferred 3 weapons are the Cruel Fire Axe, BBQ Shovel and the Savage Nail Gun.
Firearms - they do come in handy but are harder to obtain (then there's finding ammo), and melee weapons really are more fun to play with. Except the stun gun, at least once you gotta try the stun gun.
Character's individual fighting abilities - these are the best - always available & reliable, low cost to stamina and they're never damaged or in need of costly repairs. Achievement/skill points earned throughout the game are used to add special abilities: charging (powerful hits & kicks while running) and extra rage power -press 'z' when faced with desperate situations for something akin to ninja power!
A 'Special Infected' Boss Zombie: The Suicider
One issue Riptide has is spawning after you've saved your progress and exited the game. Upon restarting you often find you've backtracked and may have to complete the end of a quest again. Another major problem with this game is that there is barely any replay value. If you replay the game using your ready-made character, you'll start off on the island just after the prologue has ended. The characters inventory will come with you, and there's nothing new to do. However given the success of Riptide and its original version, Dead Island I have a feeling we're going to see many more expansions of this game.
All in all Dead Island: Riptide is one hell of a game... A skull crushing, limb slicing hell of a game.