Can you provide some examples? It seemed to me that they overtly changed very little, and mostly just opted not to mention any inconvenient old lore, which allows veteran fans to mix it with the new setting if they want. (Unlike Ravenloft, which was pretty blatant and comprehensive with its setting changes, and isn't very compatible with the old stuff.) But some folks seem pretty upset with the book regardless, so I'm wondering what I missed.
There's plenty of examples. Most of them are in the history or background lore, or are just unspoken as the base assumptions of D&D have changed over time. And to be honest, most of them don't bother me very much, although everyone has a different annoyance threshold and different hot buttons when it comes to that sort of thing.
Off the top of my head, from a purely plot/lore standpoint:
- Soth caring at all about the War of the Lance before Kitiara shows up and piques his interest
- metallic dragons being up and about at the time of the Kingpriest
- female Solamnic knights being fairly routine rather than very rare exceptions (I understand WHY this change was made, and personally agree with it, but it 100% was a change)
- good clerics/paladins getting their powers back without the intervention of the Disks of Mishakal and/or Elistan (another one i agree with, but yeah, it didn't used to be like that). Furthermore, old-canonically Kalaman fell to the Dragonarmies before Goldmoon found the Disks, so the PCs are kinda taking away from the importance of Goldmoon's story a bit
- being able to take the Test of High Sorcery rather offhandedly in some wizard's cave, rather than having to go to Wayreth
- arcane casters being able to heal, at all
Then you've got the changes that have implicitly happened as a consequence of the D&D rules changing over time. Dwarf wizards, bards casting healing, not to mention all sorts of weird and specialised subclasses with no basis in Krynn lore like Four Elements monks, or fiend pact warlocks, or Rune Knight fighters.
However, Dragonlance lore is extraordinarily voluminous, and in the vast number of words - novel and sourcebook - that have been written on the setting. you can find precedent for almost anything. Dwarf Wizard? Well, there's Willim the Black. Kender sorcerer? Nightshade Pricklypear. Great Old One warlock? Sounds like a member of the Cult of the Worm from Zhakar. Fiend pacts? Well, abishai canonically exist in DLs Abyss. Hell, I'd enthusiastically play a half-elf undead pact warlock, whose patron is the potent, bitter ghost of her human-loathing elven grandmother. And of course - the canonical heroes of Dragonlance ARE special unique snowflakes. Goldmoon is the only good cleric in the world, Raistlin is a timelooped version of the most powerful evil wizard ever, Laurana is a princess and Gilthanas a prince (who falls in love with a dragon!), Tanis and Riverwind are half-elf and ranger in a setting an edition when both of those were vanishingly rare, and 18/xx strength is suspiciously common among the fighter types in an edition where everyone was supposed to be rolling 3d6 in order. DL is a big melodramatic setting with big melodramatic larger-than-life characters who are ALLOWED to be special and unique. If you're ever going to play The Only Archfey Pact Warlock Duergar In The World Who Happens To Be A Disinherited Heir To Nobility, then a dragonlance game would be the
perfect place to do it. Special and unique is entirely in-genre.
Where you get into knots of course is that Dragonlance lore has been reinvented and the setting exploded so many times - Chaos War, War of Souls, Age of Mortals, etc etc etc, often in very poorly-received ways - that what consititutes 'canon' is more than a bit up for debate. Almost everyone mentally edits some of that stuff out when it comes to their personal canon. If you say 'only Weis and Hickman is canon' then you're stuck with the generally disliked Chaos War, and lose most of Soth's generally well-received backstory, for instance. If you stick to the modules, then you probably lose a bunch of the most memorable personal interaction and events (Sturm's death, Raistlin's taking the Black, etc) from the novels, which define DL for a lot of people. Like always I guess, around your table, canon is what you choose it to be, even in a setting like DL where canon already exists in vast amounts.