I have been playing GW2 almost 4 -5 hours a day since release and, although, I love the game i find that it lacks some pieces of an MMO, while it excels at other aspects. For quick reference on my MMO experience; SWG, WoW, Eve, EQ1&2, and DDO. These are one players opinion and everyone is welcome to their own lets not turn this into a game versus game thread.
GW2 Pros:
1. Art and game aesthetic in GW2 is probably the best in its genre, it is very consistent and fluid through the entire game. Zones are done with pain staking detail and there is very little "recycling" of textures. The art team at Anet gets a tip of the hat from me the game isn't bland like some other mmos on the market to day and it brings life to the game world.
2. Class diversity, in GW2 a Mesmer and a Necromancer are two largely different classes, even though they are both caster arch types they play extremely different. This is true of most classes in GW2 and is refreshing to see the developers have unique abilities based on class rather than cloned abilities with different animations.
3. Player driven entertainment. In most MMO's entertainment comes in whatever form the game present to you as "right." GW2 takes a different approach, it gives you all the options up front and says hey go pick what you want to do. Its the only MMO that I've played (with the exception of artisans in SWG pre NGE) that you could level to max without EVER actually killing anything. The only gripe I have on this is theres only a limited amount of Vistas and Poi's in the game, I wish you could review them (with an xp award) weekly or something to give players a reason to go there twice.
4. sPvP. Not FANTASTIC but its fun, if your tired of WvWvW give it a try. It gives you hope.
5. Content difficulty, while you will see this in my cons sections as well difficult content is productive for and required for any good MMO. Anet understands this and the scaling system is a great way to keep content relevant and your player base busy.
Cons:
1. Content difficulty, while it is good for keeping your players entertained there is a point to where the content isn't difficult for the right reasons. For example in AC there is an event (in option 1) where you have to kill 6 burrows as they spawn. I was soloing a burrow at the same speed as my 4 other teammates not because I'm better than them but because Anet has managed to make the WORST POSSIBLE hit-boxes in the universe. This kind of difficulty isn't fun for your players its frustrating. Also, I'm hoping scaling is still being tweaked because even scaled down in zones I (as a warrior) can 2-3 shot mobs where my necro friend hits like a wet noodle on the same mob.
2. There just plain isn't enough to do right now for hardcore players. I already have 100% map completion, my full Exotic set (in the style I like) and have completed every jumping puzzle in the game. I'm working on my legendary right now but the ONLY difficult part about that is raising the gold since you can essentially buy it if your rich enough. I log in and go run a farming circle around Orr and then log out, play 4 games of LoL (to pass the time it takes orchiarium to respawn) and re-do my farming route.
3. WvWvW. Its abysmal (in my opinion) it lacks the depth of GW1, all you really do is watch two huge clusters run into each other and see who has more AoE (or was smart enough to put down an arrow cart). Assaulting any structure is the same, kill the boiling tar pot, put down ram (oh no they have a catapult on other side, put down balista), if you don't have a cluster with more AoE hit you, you win. They need to add something more to WvWvW for it to be interesting. I mean heck even if they added enemy player clipping (where you could actively block people) it would have a billion times more strategy.
4. Glitches. I mean your last boss was glitched. People always bring up Deathwing from wow and say "if he was glitched" and people always counter with "Arah is not a raid." No, just no. I don't care if its Bowser from Mario 64, to Deathwing, to a Kryat Dragon in SWG. If its the highest level thing in the game MAKE SURE IT WORKS. And yes I know of the lvl 500 dark jedi in SWG but he's just an a-hole so I don't bring him up.
5. End game is "cosmetic", but there are a total of 54 different heavy chests pieces in the game from 1-80, and of those 54 they aren't even unique. For example "Duelist Patrol Breastplate" and "Tor's Chain Coat" are the EXACT same model. I'd love for someone to compile images of all the heavy armor available (as many are missing) so we can see exactly how many options we really have, I fear its far less than we expect.
6. Time investment reward. Some tasks (dungeons for example) have you sink 20-30 minutes into them an you get crap, I only run them when a guild needs help now because if I farm for 20-30 minutes I could make 1-3g and buy an item thats actually worth something. I'm not saying we need an exotic on every run, but would a rare every 3 or so be nice? You bet.
7. Dynamic events. There is nothing Dynamic about any of them they are literally ALL zerg objective, kill monster, profit. I'd love to see and event where 5 people have to stand in certain spots and make some careful jumps, or play a game of simon says, or whatever. Monster Zerg is just repetitive.
TD;LR
GW2 while a great game has many flaws, is it revolutionary? No.
Is it a good buy? I'd say so.
Will it replace your MMO craving? Unfortunately I don't see that happening in the long term.
That being said I'll log in tomorrow morning to do my Orr farming run...