As an avid MMO player, playing anything that doesn't require a subscription lends to a very negative connotation to start. We have all played F2P model MMO's that end up being more of a pay2win or nickel and dime you to death to play the game model, but that is definitely not the case in Guild Wars 2.
Guild Wars 2 is a pretty amazing fantasy MMORPG, and to make it even better you buy the game, and thats that, no monthly payments. Typically this leads to a very bad deal for the player, as they usually are so limited that its simply a demo until they purchase extra characters, the rest of the story, new zones, and gear that will let them have a chance of completing anything. While there is still a cash shop in GW2, it is mostly appearance items that people can buy if they have money to waste.
The nitty gritty of the cash shop is this; mostly cosmetic, a few convenience items, but no pay2win "super gear" for those willing to blow wads of cash to be "leet" ingame. You can buy a few things that are nice to have, like extra bank space, a new hat, or maybe a pet that follows you around looking cute but you certainly aren't going to pay your way to super hero status.
Guild Wars 2 plays much differently than most everything else on the MMO market right now. It is not a WoW clone first and foremost. You do not gain most of your skills by gaining levels, rather by using weapons available to your class. As you kill enemies with each weapon available to your class, new weapon specific skills unlock. Not only does this mean you can figure out how a class operates very early on, but you can completely change how your class works by switching weapons.
Guild Wars 2 also completely annihilates the ability to "ninja". Ninja, meaning to steal gear, kills, monies etc either by abusing loot "roll" systems, or "tagging" mobs before another player can. If you fight, you get experience and loot completely separate from other players involved, so not only does this remove much of the drama in other MMO's over who the kill or loot rightfully belonged too, but it actually promotes random people helping one and other leading to one of the most positive social experiences available in MMO's today.
With five races, and 8 professions (classes) to chose from, each having different story element choices, as well as player selected options during creation, the story line is very well done in terms of MMORPGs. Questing is also much improved from the WoW model by getting the quest simply from entering the area of the quest. When questing there is no "kill 5 pigs and steal 8 loaves of bread," instead a player is told, for instance, that they are in a Centaur stronghold and should kill centaurs, destroy their supplies, heal allies, or damage siege engines and doing any of these fills a progress bar that completes the quest. Each zone also has random events from guarding caravans, elite bosses, and raids from enemy NPCs making each zone interesting and always leaving something to do. Also zones may "scale back" a players level so that you never have a level 80 going around farming level 10 boss spawns, because the game will scale their level back to a reasonable level.
PvP in Guild Wars 2 is also very impressive. You have two options, standard PvP matches that are instanced fights between even teams, or WvWvW (world vs world vs world.) Standard PvP is separated from the rest of the game with its own leveling, gear, and vendor systems, so there is no grind leading to max level only to be destroyed in the new "bracket." WvWvW is truly amazing for those who like large scale battles. For those who don't already know, it is three servers all battling in a massive zone consisting of several regions. Battles an literally involved hundreds of players all fighting at the same time to control keeps, castles, and resources. Not only is WvWvW massive, entertaining, and ongoing, but it also effects your server as well. If your server is doing well in WvWvW you will get benefits from xp boosts, better chance to find rare loot, etc.
There are a few "downsides" most of which really come to the players preferences. Everything is account based, meaning all of your characters are in the same guild, on the same server, share a bank etc. This may or may not be a downside depending on your perspective, but is is good to know ahead of time. Lastly, you start with five character slots, and can only have one server that your characters are on, so if your the type to have 25 characters on 8 servers, you may be disappointed, but this is understandable since you don't pay extra to keep server costs going.
If you are looking for a new MMO that is different but won't require you to have a huge learning curve, that is innovative, and has some of the best PvP around all without paying $15 a month than Guild Wars 2 is your game. It may not be perfect, but its pretty darn close.