A little context for you - Falconer arose from the ashes of a band called Mithotyn, which was a folky viking themed band from the '90s, that really was ahead of its time, doing what eventually got very popular in the 2000s when the PaganFest tours started popping up. Regardless, Falconer has always retained that folky vibe to their riffs (even in the absence of the folk instruments like you'd see in bands like Eluveitie or Svartsot). This means that when they popped up in 1999, their albums were a little bit different (in a good way) from the Hammerfall and Stratovarius power metal stuff that was gaining traction in like 1997. So Falconer's early material became "classic" very quickly, and the band still plays quite a bit of material from the first two albums. I think they hold up really well; songs like "Mindtraveller," "A Quest for the Crown," "Enter the Glade," and "Clarion Call" are unstoppable. So those first two albums are pretty essential.
I like the two albums with Kristoffer Göbel well enough (I think the song "The Coronation" is one of the best the band has ever done), but Mathias is just "THE VOICE," and when he came back for Northwind, that album was like right on the mark. It's actually the full album I go back to and listen the most, and when it's at its best I think it's the best material the band has ever done - the title track, "Perjury and Sanctity," "Fairyland Fanfare," "Waltz With the Dead," etc. etc., are all fucking SPOT ON.
I also think the newest album is up there with my favorites too, because certain songs are just crazy catchy. "Halls and Chambers" might actually be my favorite song the band has ever done, and that's crazy because I've listened to Clarion Call about a billion times and it never gets old. But the title track "Black Moon Rising" has an awesome chorus and the song "Wasteland" almost sounds like a black metal song at first, it's so intense.
So if I had to rank the albums in order of my favorite to least favorite:
Northwind
Chapters from a Vale Forlorn
Falconer
Black Moon Rising
Among Beggars and Thieves
Armod
The Sceptre of Deception
Grime VS Grandeur