Profession mechanics. Then you unlock specializations, which allow you to slot specific passive perks that can reward different playstyles within that profession. And no profession is tied to one of the specific trinity. You can build most professions to DPS/Tank/Support. expansions cost, and do
Add more options. It's a 12 year old game, but still thriving with regular updates. They just introduced homesteads in the last expansion where you can build and customize a house, and have a little area to interact with your mounts. Also, killer mount system.
Oh! almost forgot, certain classes get real creative with weapon use. Like there is a profession that uses the greatsword as a ranged weapon. The staff, which is usually a ranged magic weapon, in the hands of one class is a martial weapon designed to make them bounce around.
Because I felt like adding more: SUPER welcoming community, the certain experienced players can get themselves a little "apple" icon on the minimap to show they are willing to show newbies how to do the big meta events and such. Also, respects your wallet. no Pay-to-Win crap.
and while there are occasional balance patches nerfing or buffing stats on armor (usually they target profession skills) Level 80 is the level cap for the game, and armor doesn't go beyond that. They have only ever added one additional tier of armor/weapons: LEGENDARY, which has the same stats...
as the previous highest level, but have cool animations when unsheathing, and tons of quality of life benefits, so you could restat from a DPS roaming build, but then go to raid and switch to tank or healing stats. also, there is a reason the end game on this game is called: FASHION WARS 2!
OH! I forgot the 5 different races! bog-standard humans, the Towering Norn, the diminuitive yoda-looking Asura, the plant folk Sylvari, and the horned feline Charr. each race will change the first thirty levels or so of play based on things you choose during character creation.