Three things pop instantly to mind:

ESO is the most beautiful MMO on the market, in my opinion.

The crafting system is actually -useful-, unlike many games.

My wife and I can play in the Tamriel together.

I love being able to play a TES game in a larger world with friends. Beautiful environments, familiar stories, great humour and dialogue with a fun combat system and lots of things to do around every corner.

I love that ESO has wonderful graphics, unlike the cartoon-y style of other MMOs.

I also love the sheer size of the world. I can wander around for hours and hours and still notice new things, and just marvel at the beauty.

Oh, and the player base is nice too. It's fun to come across players of all different kinds.

I love the fact you're not limited by your class.
Mages can tank, Nightblades can heal, etc.
I'm also in love with the active blocking and the fact you're limited to 5 skills and an ultimate.

Let me count the ways....

1. The Graphics - Sometimes I just stop in Aww at a Scenic Site or Awesome Lighting in a Dungeon.
2. The Look - It has a sense of Realism. There are no big Shinny Glowing Weapons, no Weird Pink and Purple Mounts, or no over Exaggerated Character Models. Thank the Divines.
3. The Skill System - Being able to play how I want, whenever I want without making a new Character is Priceless.
4. The Combat - Watching the fight instead of a cooldown on my hotbar is very Engaging. 6 hotkeys bound to my Mouse makes Combat very Fluid. 6 Hotkeys, not 50 but 6.
5. The Quests - It feels like I'm Experiencing the World rather than just Leveling Up.
6. The Story - Main story, Mages Guild Story, Fighters Guild Story I loved them All and can't wait for More.
7. The World - The Elder Scrolls Games are my Favorite games to date because of the Worlds they created. For me this game lived up to those Expectations.
8. Exploring - Yes, it is not exactly like past Elder Scrolls games, but I get travel around Tamriel. Can't do that is Skyrim.
9. The People - Ever since Morrowind I thought to myself, "How cool would it be to do this with other people"? Now I can.
10. Daggerfall Covenant - hehe

1. Graphics.
2. The fact that they are adding new content quickly, not every year.
3. The RP Community.
4. Fact that I do not need to choose a "realm" to play with my friends.
5. The game is getting better each month
6. And of course, the fact that even those who "hate" the game come here and keep discussing about it because they just can't admit that it's awesome!

What a pleasure it is to stumble upon a cheerful thread of what people LIKE, instead of the endless complaints (even if those complaints are justified). I've played this game since beta and still loving it months later, still finding new things, enjoying a bit of RP with my vampires, etc.

When my sub runs out in november, I'm considering re-subbing as the game is still a great deal of enjoyment for a retired old fogey like me! Keeps me occupied, you know!

Sorry, it's a few more than one...

1. It's not WoW
2. It's beautiful
3. It's really good fun
4. It can be challenging instead of faceroll (although I disapprove of them nerfing vet content)
5. It reminds me of Ultima Online
6. The crafting systems are engaging, fun, and most important of all, produce useful equipment
7. PVP is fun, Cyrodiil reminds me of the Lost Lands from UO and I love that I'm not forced to play in a restricted way, I can go where I want and team up with as many or as few people as I like
8. PVE is fun - the quests are interesting and entertaining, with nods to modern issues and diversity and whatnot. It has gay and lesbian NPCS. It has racial diversity. The first time I saw an NPC who'd had their eyes ripped out I was genuinely shocked.
9. The lore is rich and interesting
10. The controls are simple and intuitive and for the first time in 15 years of playing MMOs I don't actually need to use the extra 18 buttons down the side of my keyboard
11. The freedom of choice on abilities that I use, and the onus being on me to work out what suits my play style

I've said to many friends: you don't realise just what a poor standard you've been putting up with from other MMOs until you dive into a refreshing non-WoW clone like ESO and have your eyes opened for you.

The game is stunningly beautiful. The world designers deserve all the praise I can bestow upon them as every zone is a feast for the eyes. I constantly find myself looking around and being impressed by everything I see.

Customer Support does a first rate job. The few times I've needed to contact them, they reply quickly and professionally. I feel like they take the issue seriously and that they actually listen. I've never had to wait for more than an hour (may have been shorter) for a reply, unlike in other MMOs where I literally had to wait days for a response.

Also, I love that the dev team listens to player suggestions. I was hugely impressed that practically all the issues I brought up during the beta were addressed in some way. I'm very excited about the new content coming up. I can only imagine what awesomeness is on its way in the coming years.

I like the music a lot.

The world, the graphics, and the music, but mostly the stories! Some of the quests and questlines I've come across gave me great joy or sadness, and some just left me laughing hysterically. Part of the reason the stories are so good is that the game has some really great NPCs.

My Favorite Things(ESO edition)
Raindrops on Nirnroot and whiskers on khajiit
Bright copper pauldrons and warm woolen hand guards
Dead necromaniac cultists tied up with jute
These are a few of my favorite things

Diamond colored mount and crisp apple sweetrolls
Dungeons and dual wielding and recipes with plump worms
Wild Dragon Knights that fly with the moon on their wings
These are a few of my favorite things

Girls in scale armor with blue satin tabards
Bosses that stay on my screen and my slashes
Elite monsters that leap straight right at me
These are a few of my favorite things

When the werewolf bites
When the one shot stings
When I'm feeling sad
I simply remember my favorite things
And then I don't feel so bad!

Cyrodiil is a sort of a massive medieval battleground sandbox, where every day when you log on there is a different narrative going on.

I love the graphics, combat, pvp, pve, attention to detail, for example: reflections in windows when you cast skills, different footstep sounds ( skeleton costume has it's own footstep sound ), horses start out slow for the first second or two when you ride them ( one of the things I hated in WoW was when you started moving, your mount immediately started running at full speed.. It made it seem choppy)
Pretty much everything about this game except that it really needs arenas or a duel function.