If you come to this trilogy because you are interested in the Mystara world, you probably will get annoyed at the liberties the author took.
However, if you 1) like intelligent dragons as important characters (particularly in books 2 and 3), 2) don't mind some standard fantasy cliches (not especially bad here, really), and 3) are willing to let the books stand on their own (rather than as part of the Mystara mythos), then you'll probably like this series a lot. The plot relies on standard fantasy tropes, but the story actually goes in some fairly unexpected directions as the trilogy progresses. The series is considerably less derivative than it initially appears.
Regarding other reviewers' complaints:
-The main character's invincibility: Yes, the armor of the dragon lord does make the main character ridiculously powerful. However, that's kind of the point. The armor is built up in the story as granting incredible powers to fight dragons. Whether the main character gives up that awesome power is pivotal to the plot: he doesn't want to be vulnerable, but he doesn't want all dragons to fear him unreasonably, either. Also, in later books, he faces much higher odds, and comes close to death multiple times.
-Dragons' "personal space" issues: this trait is not handled as inconsistently as another reviewer said. This trait was very much a "personal space" (very close proximity) issue more than unthinking territoriality between dragons. On the whole, the author did a great job establishing dragons as intelligent beings, while still differentiating them from humans.
Overall, I've read a lot of fantasy novels, and while I wouldn't put this trilogy at the very top of the list, it was still quite good and completely worth my time. If you like fantasy novels about dragons, you could do a whole lot worse than the Dragonlord Chronicles.