Haypi Kingdom has taken many of the main elements of other very popular browser based games, most noticeably Evony with traces of other games such as Travian and the like.  The game starts off by giving you a series of beginner quests, all which reward you with resources or gold.  Your main goal in the beginning is to grow as fast as you can.  Each time you build, train a troop or kill an enemy troop you get ranking points suitably named "prestige".  Since prestige is what dictates your rank, and rank is the only gauge other players have of you, raising this number is important as a player is less likely to attack someone with a rank level much higher than their own.  Also many guilds will only accept you based on your rank.  When you finally build up enough and have a small stack of troops at your command, you can begin attacking other players and killing their troops or taking their resources to use for yourself.  In all browser based games of this nature, being aggressive and attacking others is the quickest way for you to get ahead of everyone else.  If you look at the leaderboards in each of these games you will find the top players are usually the top attackers as well.  You can choose to play peacefully amongst your neighbours, however this usually leads to an uneventful existence and most likely the target of attacks.

Haypi Kingdom seems to have been based on the popular browser based game Evony which first drew attention to itself with banner ads of well endowed women wearing very low medieval gowns, which to the chagrin of many players were nowhere to be found in the game.  Since Evony requires flash be installedand Apple refuses to support flash in the Safari browser, Haypi Kingdom is a good alternative.  Haypi Kingdom boasts a chat system similar to Evony where you use world chat which everyone online can see, private chat or guild chat.  There is no shortage of "regulars" in Haypi that seem to patrol the world chat all day however some of these regulars can be assigned as experts by Haypi staff which signify that they are veterans of the game that could provide expert advice, as well as being bestowed the ability to temporarily mute another player who is causing problems or breaking any rules in world chat.

To progress to higher ranks your must reach certain levels of prestige.  Because of this prestige is more sought after than any other resource or treasure.  Since you cannot get prestige by attacking a player and taking resources, you must kill their troops to receive any prestige.  You will find that many large players will only attack another player if they have large amounts of troops to kill.  The troops in Haypi are fairly unbalanced as well with catapults being largely more powerful than any other troop,  and given their range can kill another player's entire army without a single casualty.  If you've taken weeks to amass an army just to have it wiped out in 1 attack, you can imagine the frustration this can lead to.  After an attack like this many players end up abandoning their cities not wanting to invest all that time again to recover. 

The marketplace where you can sell or buy goods and treasures

Players have the option of using real money to purchase basically anything in the game they want. Players that are willing to spend an unlimited amount of money have an edge so great that there is no way you can compete with them. To put it into perspective, you can use real money to purchase resources. Those resources can be used to train troops which you can finish instantly again using real money. If a player spends enough money they can amass a huge army in minutes where it would have taken you weeks to do. There are players out there that will spend hundreds or even thousands of dollars (seriously) on a game like this.  This huge gap between real money players and regular players is one of the biggest setbacks of the game.  Granted Haypi Kingdom exists to make money, but when the paying players are so far ahead of everyone else it upsets the balance of the game. 
When you finally max out your villages, have destroyed everyone around you and are a member of a successful guild you will find there is very little to do as there is no end-game content.  You will basically attack just to keep your troops from starving and wait for a war to begin.  The Haypi servers never reset and it seems like you are left to either quit and restart on a new server or continue a pointless existence in a barren wasteland of inactive players.  If they followed the mould of Travian, which gave players a goal and the opportunity to win the server, Haypi would be much more enjoyable.