There is info about this in one of the stickies here, but in a nutshell:
- there are few top level dungeons (5man) with explorer mode which is THE hard difficulty where you can get very unique skins for your armour and weapons
- multiple massive elite DEs in which you can participate, it actually involves quite a long chain of smaller DEs where you work on achieving the goal (unlocking world boss) with other people. Everything works parallel and simultaneously, for example there are few scattered events accross the zone which have to be completed to unlock the next phase, so it's NOT like you are doing "event a-then b->then c" etc, all those events can be completed at the same time. So for example your guild can send one group to defeat the cultists and the other one to build catapults.
- elite high level zones, where you can find top crafting recipes/materials, karma (non trade-able currency gained through completing DEs) vendors with more unique skins or consumables
- achievement system with many, many different challenges rewarding titles, pets, skins and all the vanity stuff you need
- basically whole game is an end game. Remember how in WoW when you reached max level, but missed few zones and didn't have incentive to go back because one-shoting everything got bored very quickly? In GW2 you are scaled down to the level of the zone you are in, so while you still have small advantage by having new skills you didn't had before, you can't go around killing everything with farts - content stays challenging. Plus, you can change appearance of every weapon armour so if you liked that sword in low level area, you can go there, get it and use it cause you can transfer the stats - all this while you feel you achieved something because the content was still challenging
Actually there is much more, like: exploration, crafting, mini games (bar fights!) etc. So no, you will not be bored at max level
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