If LotRO is too mindless and dumbed-down MMOs are your bane, then head straight to DDO! It is easily the most complex MMO out there, free to play, and a a great deal of fun. Nothing comes close to the truly insane character customization it has.
DDO basically starts with D&D 3.5, so out of the gate you can have multiclassed characters. So unlike a typical MMO where you're a tank or a caster, in DDO you can literally play a fighter for 10 levels, play wizard for 6 more levels and then play 4 more as a cleric, and have the skills from all 3 at the same time!
From D&D you have the Feats selection, then on top of that, each class has multiple enhancement trees. Currently Wizard has 3 different trees, and you can choose enhancements from any of them. If you're multiclass, you can choose from ALL the enhancement trees for each class, and there's also a racial enhancement tree, so a single character could have as many as ten trees to choose from! And each race has it's own impact on your character as well.
But wait, there's more! Turbine's gone past level 20 ("epic levels") and characters also have epic destinies - yet another enhancement tree system. There are 8 of those, one for each class, but you can choose whichever you want, so you can be a lev 20+ fighter with the druid tree active! You can also also "twist" 3 of the skills from any tree into whatever you're doing, so your fighter can have druid enhancements, and twist in a couple rogue enhancements at the same time.
[shamwow voice]But there's STILL more![/shamwow] And, just because you don't want to be a cookie cutter build, you can also opt to kill your capped character and resurrect them, True Resurrection, which gives your character a permanent past life bonus. In fact you can 3 times .. per class! There is even a feat "completionist" for people who've played and TR'd as every character class. And there are truly insane people in the game who are trying to do that three times for every past life buff in the game.
Of course a fighter/wizard/cleric would be a pretty poor combination, and having druid active may not make sense. Nothing stops you from making a truly gimped character in DDO, and new players generally shouldn't multiclass, but a good way to see the insanity is to check out the DDOracle. It's currently out of date, but look at the what people are playing, in particular the top multiclass combos, and race/class combos. Note there's also a least common multiclass list as well, which is often amusing.
DDO does a good job of being D&D. It's quest oriented, not grind oriented, and XP is based on completion. One of my favorite features is the dungeon master - as you're crawling through a quest, there's a DM voiceover that adds a lot of D&D feel. The other thing DDO does is TRAPS! This is not WoW - dungeons have traps that can and will kill your character instantly on high difficulty. Respect the trap! Take a rogue. Or a cleric that can rez
What DDO doesn't get you is PVP. It's D&D - you versus the dungeons, monsters, pirates, demons, undead - anything but other players. There is an extremely limited brawling facility in taverns and that's it, and no griefing. Adventurers quest together, in parties (up to 6) or raids (up to 12). Evil alignment is not available - True Neutral is as evil as you can get. And everything is instanced, so only in public areas (towns, taverns) are you running past other players -- there are no WoW style 200-person fights around Tarren Mills.
DDO is free to play but there were two paid expansions. Simply playing the game earns you points that you can spend on expansion packs, and in theory you could play long enough and simply earn all the game content. In theory you might be playing when you're 80, too. There are enough points to earn that you'll get expansion packs, but in practice people generally buy at least a few as each pack gives more opportunities to earn points.
Looking over this, I realize it probably sounds insanely hard to play, and it's not. It's D&D. You can just get the client, roll up a paladin and start banging heads all the way to cap and have fun. But there's enormous depth to DDO, and that's what makes it fun. If you want to go farther, ddowiki.com will be a bookmark. But gameplay here is a little different. In most MMO's you play the content, get sick of it, and then wait for new content. In DDO it's almost more like golf, where each quest is a golf course that you visit repeatedly, and the real focus is on your character and your game.