DISCLAIMER: Comments below are based on my personal playing experience. Results may vary between users

After reading the OP here:
http://forums.elderscrollsonline.com/en/discussion/211200/im-not-loyal-to-eso#latest
and seeing a lot of bitching and whingeing from little princesses in the Server Down Again thread, I thought now might be a good time to say how much I love ESO.
Ever since I started playing ESO, I've been raving non-stop to a couple of my gamer friends about how much I love it and why they need to start playing. My nagging has paid off and both are set up to play. *happy dance*
Why ESO is my fav MMO (in no particular order)
* Zone chat is not full of spam. There is occasional trade spamming, but not to the extent seen in other games. Not to mention the scammers trying to sell game currency etc.
* Douchebaggrumpypants peeps are minimal. Sure we've all encountered someone who ended up on the ignore list, but the for the most part ESO players are a friendly, silly, helpful bunch of folks.
* Pay to win not a major issue: I understand a lot of people might disagree with me here, but for the most part having a fat wallet has no excessive impact on character advancement. You can't join ESO as Lvl1 and immediately go buy the best weapons, armour etc. Those things you have to work for. Even if you are willing to pay for them, you have to make the gold to buy.
* Play your own way. PVP, PVE, Crafter, Fisherman, Trader. No penalty for playing the game the way it makes it fun for you.
* No subscription required. You can pay once and never spend another cent on the game if you really want to. I believe this makes the game more affordable and therefore more accessible by more players. (Even fiscally challenged folks like me) As a side note, I think the cost/benefit of ESO+ membership is pretty fair too.
* Grinding is not a necessity to level up. You can do it if you want to, or to farm or whatever; but you don't have to spend hours grinding on mobs simply to make the next level. ESO provides so many ways to gain XP that levelling is fun not a chore.
* Absence of incessant patching updates every time you launch the client.
There are a few other things, but I think that's enough for now. In conclusion, ESO is the first MMO I've tried and played without quitting in the first month, that to me says everything.