[Update #2]: Guild Wars 2's October 4th update will empower old specializations and rebalance classes for PvP.
[Update]: Tower of Nightmares, Guild Wars 2's long-lost Season 1 episode, has now been reborn
After many years of rumors and teasers, the day has finally come - Guild Wars 2 has now made its way over to Steam! Much like the standalone version of the game, all of the base content in the Steam edition of Guild Wars 2 is entirely free to play. After you're done with that you can continue your adventures by grabbing the Heart of Thorns & Path of Fire expansion bundle, going for the newest End of Dragons expansion, or the freshly added pack containing all of the Living World mini-episodes. Personally, I'd stick to the main story and go for the double expansion bundle first.
Since this is also Guild Wars 2's tenth anniversary, ArenaNet has unleashed a bunch of boosts for both PvP and PvE content, as well as a new set of achievements for both veterans and newcomers alike. These new achievements will guide you across the entirety of Guild Wars 2's world and offer you a chance to score a bunch of fancy new armor and weapons.
While the Steam release has definitely stolen the spotlight, this update is also significant because it brings with it a massive amount of balance changes to some of the often-ignored classes and specializations. There's still some more work that needs to be done before we're really there, but thanks to the balance tweaks the damage difference between some of the power (direct damage) and condition (damage over time) builds has been greatly shrunk, which should hopefully result in a much more diverse and interesting meta.
There's far too many changes to go over in brief, so if you're interested in all of the details you can find what you seek over at the official patch notes.
As for the freshly released Steam version, I would highly recommend giving it a try if you have even a passing interest in what Guild Wars 2 has to offer. I've been playing it on and off for many years at this point, and the best thing about Guild Wars 2 is the fact that you can play for as much or as little as you like without being punished for it, which is unfortunately a bit of a rarity in today's MMO world.
My little musings aside, you can learn more about Guild Wars 2, as well as check out some of the new player reviews, over at Steam. Enjoy!