Superficially, the changes sound pretty friendly to players. We have vague language promising better random legacy traits that we won't be able to evaluate until the system goes live. There will be ways to make non-random improvements to existing weapons, replacing worthless legacies with stat boosts and upgrading the "quality" of important legacies so that they don't cost too much to upgrade. They're also tweaking the exp curve to make lower quality legendary items level faster, while increasing the exp required to level the raid-drop 1st age weapons (think Epic or Fabled quality in WoW or EQ2 respectively). But what hasn't changed?
Legacies are still random
They concede that it's a problem for players not to know whether a weapon is worth leveling until after they level it a bit to see if it picks up a crucial missing legacy. (In fact, they're overhauling the whole legacy pool for Champions because our weapons live or die on whether they get the legacy that boosts DPS for your preferred stance.) Now the strongest legacies are most likely to be handed out when you initially level the weapon.
The catch is that they're not willing to give up the slot machine. There will still be "a small chance" of getting one of the more powerful "group A" legacies later in the weapon's life. Even if you don't get quite that lucky, there will always be the chance that the RNG outdoes itself with the ideal assortment of "group B" legacies. Don't you want to spend time grinding out more exp on that weapon that's almost as good as your current one, just in case?
The Existing Relics are probably still random
Turbine is adding a fourth relic slot and allowing crafters to make relics that go in it. That's great for crafters, since players only needed a single crafted weapon back before Moria, and now they'll need replacement crafted relics every time they switch disposable advance-able "legendary" items. Or at least, that would be the case, except for the minor fact that they have also decided that they're jealous of WoW's self-only crafter perks. Don't you want to grind out a profession for no real financial benefit so you can have the best bonuses?
What they don't say very much about is those other three slots, which will still be filled using the deconstruction pyramid-scheme slot machine. These relics are still untrade-able, so you will have to level and then deconstruct large numbers of items to get them. Don't you want to go level more legendary items so that you can have a random chance to get the all-new tier 9 relics?
(Currently, each tier is made by combining five of the previous tier. If they stick to that exponential progression, a single random tier 9 relic will result when you combine 1.95 million tier 1 relics.)
Most of your item experience will be wiped
Hidden away on the third page is the revelation that Mirkwood-quality (level 61+) weapons will not accept item exp runes from previous content. Runes are the consolation prize for constantly replacing your supposedly "legendary" named advance-able items; you don't just have a random chance of getting relics, you get to transfer some of the exp of your old weapon over to your new one (possibly helping you leapfrog a few levels to figure out if the new one is worth owning in the first place).
If you're using a 3rd age weapon, like the ones that I have access to currently, you're simply out of luck. Your Moria quality runes are good for leveling Moria quality weapons to break them down for relic parts and nothing else. If you happen to have a raid-quality 2nd or 1st age weapon and you maxxed it out at level 60, you can get a Mirkwood rune instead. In case you were expecting a lot of experience out of that deal, Turbine clarifies:
Please note that the Mirkwood heritage rune received from these deconstructions will be a rune of lesser experience value than the Moria heritage rune received.
Don't you love leveling disposable legendary items so much that you're happy to be starting over from zero exp every expansion?
The Sacred Cow: Timesink, Timesink, Timesink, Timesink
I probably wouldn't be so hostile towards this feature if they hadn't misleadingly promoted it with reference to the ACTUAL legendary weapons of the Fellowship of the Ring, which they didn't discard and replace with random items from every orc they killed because these items were actually legendary. Indeed, they initially described the items as "mobile quest hubs", where players would get quests to do things that would improve their existing weapon.
Instead, the primary design feature of this system has been to get players to spend more time working on weapon after weapon without actually having to add new content to support that extra grinding. The changes try to paper over the community's complaints with vague promises that this expansion's weapons will be "better" - of course they will, or players would not abandon their current ones.
At the end of the day, Turbine's item advancement system doesn't really detract from the game - they've still implemented a high quality experience that I'm happy to play through at least once. At the same time, the sheer disposability of the not-so-legendary weapons removes all incentive to actually work on any of them, when the system is so clearly designed to wipe out as much of that work as Turbine thinks they can get away with, as often as Turbine thinks they can get away with it. Legendary items could have been unique and exciting; instead, Turbine has reduced them to just another timesink.