1.its free(only for membership you must pay but they play on servers for members and you for free so that doesnt matter)
2.a BIG world
3.a good tutorial that leads you trough all skills and things you can do and some itemcombinations
4.i think over 10000 items and almost all of them you can create(you cant create secret or quest-items)
5.pvp worlds and a duelplace for 1 vs 1,you also can fight for the enemy money
6.i think over 30 skills(i dont mean only combat skills),like atack,defend,magic,strengh,bow,fletch,woodcutting,cooking,firemaking,fishing etc.
7.a grand exchange where you can trade with everyone of the worlds and servers at one time
8.trade with other players players exactly when you see them
9.team up with others in quests against strong enemys or hard puzzles
9.3 gods wich name i dont know now
10.everywhere on the map are things for decoration and all decorations,items and so on have their own description
11.buy many items(like 3 millons),wait a day and the item is worthing more so you can sell it
12.many kinds of foods and some elixiers for healing your character
13.build your own house or get an animal thats defending you(only for members)
14.the world is big,but members got a 3 times bigger and double quests
15.graphic is 3d but not so good
16.not many quests but they are realy fun
17.secrets that arent in quests so find out by yourself and get secret items or weapons
18.go in the wilderness to fight strong creatures and go trough it to go to even stronger enemys
19.get skills up to 99 and join gulds when you are good enough
20.some tools:friendslist,clan,noticebook,goals,a tool to find out the worth of an item
21.EVENTS all few months,get special items and experience there
22.if you dont want to train or explore the big map you can go play those minigames like bountyrun or capture the stone of one of those gods,its realy fun
23.clanwars are also in it
24.members got many minigames that they can choose
25.sometimes you are teleported to a minigame or a quest thats realy funny(best are the quests from the world of devil bob(uncook the fish))XD
26.i think over 30 emotes to do
27.the peoples are VERY nice and will help you surely at the beginning with money and items and maybe how to do the puzzles from the quests
28.a strategy system for fighting(ranger beats mage,mage beats meele,meele beats ranger)
29.many combat skills to learn and creatures to kill with it(all creatures got description too)

at all there is some more but i cant say it all cause i dont remember everything.
its getting bored sometimes but if you reach a goal it gets realy fun again and the minigames you can play when you get bored.you can ask friends to play some games with you or dance with them or make races(new).
i played many other games with good graphics like from world of warcraft and some nice moves and strategy systems but at all they get boring too fast and there is nothing hided so you play trough the game and end of story.only a few skills are there and also skills as same as runescape.its getting boring with time because you always do the same in the quests:run there,kill those,collect this,speak to him,run here,run there,kill this….
even if you are realy addicted to it at the beginning its getting boring too fast and you search for other games.
runescape was the first mmo i played and realy the best

if there are some mistakes in writing,sorry im germany