Guild Wars 2 basically breaks down like this:
Story: 6.5/10. More to it than a lot of MMOs, rotating events which last for a season or so and can make permanent or semi-permanent changes to the game; the one that started around when I joined was a complete invasion of the main hub city which dislocated the population and services to a refugee camp/fortress and turned the city into a wrecked event warzone.
PvE Content: 8/10 on first character playthrough, 4/10 on characters after your first. There's the aforementioned events, and a lot of the PvE content is fairly varied and interesting. There's random timer-based events all over the place alongside more traditional quests. It's fairly fresh and fun the first time you play it, and you'll get nowhere near 100% completion without intentionally trying to do so.
It's also boring as shit every time after the first. Once you've experienced it once, all that PvE has going for it is farming the timer-based boss events for loot and the global events.
Thankfully the way the bosses are designed is sensible. They're not instanced or anything, everyone in a zone is working together and in contact (unless you hit the population cap on the area, which is pretty darn high, in which case everyone past that goes into a second spillover instance). As long as you use a timer-tracking page you'll have no trouble running a boss train on any of the good servers. People are generally friendly and helpful, everyone contributes to the fight, and each player gets their own loot if they contributed to a kill.
There are also a plentiful scattering of parkour courses you can find and run for decent loot.
Leveling/Building: Super fast. You can get a Warrior from starting out to the level cap in a week (though admittedly War is the easiest to level). It's also pretty easy to get high-end gear just in the course of playing, though the very-slightly-better-stats-than-everything-else-plus-super-shiny-graphics legendaries are absurdly expensive. Thankfully they don't offer much more than the stuff you can pick up for a couple GP, apart from the appearances.
Pretty much every class can be built in six ways or more, depending on how you stat them and what gear you buy. Restatting is pretty much costless and instant. Ferex, the same core "wizard" class (the Elementalist) can be built as a healbot, a long-ranged blaster, a CC monster, a melee tank, a melee DPS, and a generalist, just off the top of my head.
PvP: 5/10. There's a distinction to be made here. When someone says 'PvP' in reference to GW2, they're talking about the limited TDM/zone-capture stuff where it's 4v4, 6v6, &c. You play with special PvP gear, and I suppose some people find it interesting, but it bored the shit out of me.
WvW: 10/10. If you're playing GW2, chances are it's some combination of this and no subscription fees. World vs. World is the biggest and best feature GW2 has. It's three-way server-wide objective-based competitive multiplayer. The entire population of three servers are pitted against each other on a series of large maps. There are tangible rewards for different successes, as well as season-based tournaments that grant you much nicer rewards for completing various objectives.
That said, a big part of WvW is making sure that you join the game on a server good for it. I'll go ahead and make my pitch here: I'm on
Sea of Sorrows, a Tier 2 NA server; we were 4th highest ranked when I joined and are currently at 6th highest (though we'll be taking 5th back from Yak's Bend soon) and during the Spring 2014 tournament were consistently getting rotated in to fight Tier 1 servers. What that means is this:
1. We have a server-wide teamspeak server with channels for each WvW map.
2. Regardless of when you get on, there's going to be at least 30-40 people in teamspeak as well as at least that many pubbies, and pretty much always someone willing to pop their commander tag on and lead a group. When I was playing back in Spring 2014 we had near-100% uptime on our WvW groups because our population is split between NA and SEA; most evenings we had one commander running in Eternal Battlegrounds (the main map), another in the Borderlands, and a third in Edge of the Mists (the overflow/waiting map), each with a solid 60-70 people listening on teamspeak and that many again training behind the commander tag.
There are also a number of different ways to play in WvW; you can roll with a large group to get into fights for loot and objective-taking. You can scout and provide intel for a large group. You can build as a solo roamer and run around picking off isolated individuals. You can play a Mesmer and hide inside a tower or keep when an enemy server takes it, then use your portals to get fifty people past the gates.
There's resources and supply caravans to deliver them; you can use those to upgrade the towers and keeps you hold, or to build siege equipment. Terrain can block damage, there's a down/revive/finisher system, and everybody gets stamina-limited dodge rolls.
It's hands-down the best PvP experience I've ever had with an MMO. If you get GW2, this is almost certainly going to be your bread-and-butter entertainment. Here are a couple clips of what good WvW play can look like:
Solo Thief play,
Solo Mesmer play,
typical zergs,
small-group anti-zerg play,
Rifle Warriors: useless and hilarious.