IMHO. The fact that it's free to play after buying the box is the at the top of everyone's list. but im going to list all mine hehe.
1. F2P -B2p.
3. Awesome Looking Character's and animations not to mention Combining attacks
4. No Holy Trinity. To an extent Don't chew me out for that.
5. Massive Scale Dynamic Event's and World Progression.
6. A beautiful Unique Art Style
7. a near Perfect blending of fantasy Yet Sci-fi in one - Aura Golem's and such
8. They Specifically Stated they dont plan on competing with wow. we all know how many MMO'S have died with those words
9. The Combat System For example Dodging an attack Gives that Realistic Feeling and Makes you work for a kill instead of Mashing 1 2 5 button's all the time.
10. I like the Simple yet advanced Personal Story they implemented Makes me feel like the MMO Is Made just for me.
11. Possible to get 80 without help?. even more of a feeling that makes it seem like that game was made for me.
12. In the Press beta's and Demo's and other Game play Video's iv seen Teamwork from people just coming to help you out for the hell of it.
What Make's it Promising to me.
1. Arenanet are taking there time in developing it and Are not rushing it For $$ purposes
2. They are creating the game for the player's and are putting there best into that game so im thankful for them.
3. There team consists of people from Blizzard/Mythic/Bio-ware And other known Company's. so they all have worked on games that have failed and succeeded getting a good idea of what formula makes a mmo work.
I have many more but im just listing a few. What makes it Revolutionary for you