Whether you'll have fun in GW 2 will largely depend on what you like to do in a MMO.
If you're a fan of raid-dungeons and accomplishing large PVE achievements in a large group, then I'd assume that GW 2 is not really the right thing for you, as it does only offer 5 person dungeons and all the outdoor group-bosses I've encountered are not as challenging as a well thought out raidboss in WoW or any other game that offers PVE-raids.
And Dungeons are done completely differently because of the lack of dedicated healers. It's much more movement based and, especially at the beginning, is very difficult in comparison to WoW. But, like it's always the case with PVE, once you get the hang of it and learn the encounters, they can get really easy, if my guildies are to be believed (I don't do pve, except for lvling).
If you like large scale PVP with siege equipment etc., however, you will really like GW 2, because it does that really right with it's WvW system.
If you're more the Arena player, tPVP would be your playstyle of choice. Sadly, this is lacking some basic mechanics like a proper matchmaking system. Therefore, you'll be mostly facerolling if you're good or, if your team isn't that good yet, get facerolled, because there seems to be no tool to separate the teams based on skill lvl, like WoW's arena-system strives to do.
As other said, it's just a one time cost: no monthly fee. How do they make a profit like that? Paying a monthly fee is reasonable for an MMO.
I've been playing WoW heavily for almost a year. I started playing GW2 a bit over a week ago (for work: yes, be jealous).
GW2 is very different. Some differences I enjoy, some I don't (yet). I don't plan/expect to stop playing WoW any time soon, but I am enjoying GW2.
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Paying for the game offsets their R&D investment even if you never play for more than a month. Paying a monthly fee offsets their server/bandwidth costs. And really, what's $15 for a months worth of play if you are at all serious about it? What else can you do for that much fun that only costs $15/month?
I have one more question (i hope the last one before starting gaming :P). I wanted to buy Guild Wars 2 at http://www.go2arena.com/guild-wars-2.html but i saw there 3 products. Digital deluxe, digital standard and gamecard. Which one should i get?
The gamecard isn't the game, just an alternative way to purchase gems (with which you can buy certain items in the game).
You can see what more you get with the digital deluxe version at: http://wiki.guildwars2.com/wiki/Digi...ars_2_editions (including links to the wiki to see what these items are).
Every character gets his own copy of the Golem Banker and the Hero's Band. (So you get them once per character you create)
If I had to guess, and it's just a guess, I'd say it's about 50/50. That said, there are two things you should know.
1. You won't be disadvantaged in game by buying the standard version.
2. You can always upgrade later if you really want to through the gem shop. You can even earn gold in game, buy gems using the gold and upgrade without spending real money (if you really want to).