MMO that will suck me in?

Warframe.

What about Scarlet Blade? The game will suck you in... literally... D:

MechWarrior Online! Obviously that's a game about mech battles. Set in Battletech universe, with 1:1 timescale (every reallife day is a day in game, but like in 3059 or something). It plays great if you have premium, or buy "special" mechs but it doesn't feel like pay2win, only pay2getstufffaster, and still plays good if you don't have premium. Oh but it's not open world, you just play signle matches on different maps... think like War Thunder/World of Tanks with mechs... Just don't be suprised you won't understand shit about this game. There's ALOT of stuff to understand. But the community is pretty nice, since most kids and trolls are kept away by the steep learning curve. The whole game is a bit like mech's ArmA, if HAWKEN was mech's CoD.

Eve Online or The Secret World

Final Fantasy XIV: A Realm Reborn definitely gets my recommendation. The game is sub based, costing only $12 or $15 a month depending on whether you want 1 character per world with an 8 character limit, or 8 characters per world with a 42 character limit.

However you only need 1 character. Once you reach level 15 in the class you chose to start with, you can go to any class guild in the game and change class. Once you've unlocked a class, you can change between them at any time by simply switching out your weapon. Classes feed into jobs, allowing you to unlock more skills and abilities to use. There's currently 9 classes. 6 of which are Disciples of War, and 3 of which are Disciples of Magic. There's also 11 more classes, 3 of which are gatherers (miner, fisher, etc), and the other 8 which are crafters. As for jobs, there is 10.

On top of this, the game looks amazing. The graphics are probably the best in a MMO at the moment. The game itself is of a high quality too, thanks to the sub. New content is also constantly added every few months, and the first expansion pack is on the way.

As for end game content, the game doesn't start until you reach end game. There's tons of level 50 dungeons, trials, and raids to keep you interested for months. There's tons of outfits with unique looks for you to obtain too, meaning customisation is great.

If you have any questions about the game, I can do my best to answer them for you.

In regards to WoW, which many have mentioned. I would avoid it if I were you. Recently rebought WoW after not playing since WotLK. The game is awful now. They've changed too much and at this point are just milking the game for cash. It's a shadow of its former glory, which is a real shame.

Try Archeage and maybe wait for Black Desert.

I'm biased as I'm one of the developers, but if you're into space MMOs you can give Gates of Horizon a try. No subscription, multiple ships control and desktop and mobile access within the same persistent universe :)

Crimecraft, Raiderz, Path of Exile, WoW. You should also try MOBA games, those will suck you in too as they are enjoyable and you will want to play more, such games being Heroes of Newerth and a ZOMBA called Dead Island Epidemic. If you love cards, then Infinity Wars could also suck you in. Oh and MechWarrior Online is an amazing robot mech combat game with many players, also a good try. Ah and ZMR or Hazard Ops could be a great try.

DC Universe™ i love it, but it's my opinion :)

I've also had quite some fun with APB reloaded. it's something like GTA online.

If you like collectible card games you can try Hearthstone

It really depends on, what you are looking for in that MMO.

For me, only Champions Online was the one that could suck me in. Mainly because I've spent almost an hour making my characters the way, I want them to look like. I wanted to try City of Heroes out too, but unfortunately, it's already gone by the time I could try it.
Of course, it also has it's flaws, but which game don't have? However, CO has one of the most improved character creator (please be aware, that I said "one of").

RIFT is a good MMORPG to play, I recommend that.

Destiny

Kappa
That isn't even a MMO

Erm maplestory?
Oh and skyrim

GUILD WARS 2!!!!!!!!

DotA 2 or CS:GO,you can't never feel that you've wasted your time because all that pay-2-win and play-all-the-week-to-get-super-item strategies don't take place here.Playing it both,I really enjoy because Your Result depends on Your Actions and Teamplay,you can't lose to guy who just has registered day earlier so he has more gold,siver,platinum stuff.
Played a lot of MMO-s before but I always got stucked because you can't actually play competitive against those who have more hours of farming and more money.I don't blame people who buy in-game items and upgrades,I can understand them because they get stuck too so they can't leave because it means they've wasted too much time&cash on useless thing and they keep paying.That's how MMO get their money being F2P.

try play ArcheAge! (y)

Chiming in with the TSW crowd, if you decide to give it a spin you absolutely want to "/chat join Sanctuary"; the community in that channel is just so welcoming and helpful.

Other games I can offer my, entirely subjective, experiences with (quite the selection, considering I have to change games every so often):

WoW - If it's PVE endgame you're looking for WoW has you covered. The downside is the subscription. Well that and the graphics may take a few days to get used to.

SWTOR - Best storytelling I've experienced in an MMO for a while. As you're a fan of the franchise I heartily recommend trying it out, it's possible to enjoy the class storylines as a F2P player. If it sucks you in a subscription may be worth the money. The downside is a somewhat lacking endgame experience (as of the last expansion, I didn't get around to try the newest one yet).

TESO - It's going to drop its subscription model in a month so that's a great time to try it out. Once again it's the lack of endgame and the then broken performance in RvR that drove me to shelve my account for a while. If you want to give it a try I suggest investing a dollar in a key for the Explorer's Pack. It can still be found online and gets rid of the race/alliance lock on character creation. There's no trial version available as far as I know.

Neverwinter Online - If you take it as a purely F2P game it can be great fun. Fast paced action combat, decent graphics and it has a new module (expansion) coming up in a month. The downside is it's pretty in your face with its cash shop, though I've managed to avoid sinking more than 5$ into it to get more character slots and the first time buyers pack during the 7 months I've been playing it off and on.

Tera - It's what I'm currently trying to bridge the time until TESO's B2P conversion. It also has action oriented combat, though not as snappy as Neverwinter's, but the european publisher is terribad. Wouldn't exactly recommend it in the EU, the NA version is supposed to be handled better.

FFXIV - It's pretty, it has a decent storyline and a big franchise behind it. It also isn't for me, combat feels too slow for my taste and I'm not a huge fan of grinding FATEs (think GW2's public events) apparently the main method of leveling up your jobs (Your can have all classes on just one character, if you want. Sadly normal quests are not repeatable). If it ever moves away from the subscription model it might manage to pull me in for a week every now and again.

Wildstar - Action combat, you can in theory pay for your subscription with ingame currency. It's also not taking itself too seriously. I've dropped it after my free month was up, it's just too over the top for my tastes and didn't offer a lot of endgame aside from one raid. They offer free trials so you can test it yourself if it interests you.

Dota may be good

IF you are willing to give in the money for a sub (It looks like you are) DCUO is a cool mmo that is pretty much all end game

Why dont you give a try to Lord of the rings online?

I play GW 2 from beta to now and if you tell me there is no endgame content or other stuff then i tell ya you didnt know nothing about gw 2... still you have a lot of things to do. Like the living world story and now upcomming expansion with no raised lvl cap or new tier of gear just adding new stuff like new class or new zones or new mastery system or specializations system so sorry about that but GW 2 is fking awsome game with no monthly fees

I would recommend The Secret World. No subscription fee, the best quest design I've ever seen in an MMO and some really good environments. Just don't be of the mindset that the end game is a goal that you need to reach ASAP, the path to the endgame is very enjoyable, with well thought out quests. Also, be prepared to use your brain a lot, because many of the quests require you to actually think.

Sorry I don't play much MMO anymore. Can't provide any useful links