While I am speaking strictly from a PvP perspective, a lot of this also applies to PvE.
To be brutally honest, DK's (especially frost) is in its most boring/shittiest state I've ever seen since the class was introduced in Wrath. There are several things wrong with frost so I'll just focus on the big ones that most of us know...
1- Umm... Why Dualwield?
I am not opposed to DW Frost, but 2 hander fits in a lot more with the lore (yes... a lot of us play a class based on that surprisingly) Not too long ago (legion) a lot of the damage was based on our Obliterates and Frost Strikes, and my goodness were those big crits in PvP. I hit 2300 in 1 week of play in the final week of season 7 Legion and had a blast (before GCD just killed us) The Lich King uses a 2Hander, WE used to be able to choose between 2h frost or DW frost, why force us into DW? I am not talking about just the appearance of using weapons, my second point will shed more light on this.
2- Frost fever? Really Blizzard?
Something feels very wrong with the fact that Frost fever is the main source of damage... As of writing this post, apparently Frost DK's are really underpeferoming in both PvP (all of BFA) and PvE (since 8.1) We're just severely limited by slow gameplay and very mediocre damage, no one will even bother to play with a Frost DK if they're considering to push past 2.2k because it is a tier shit class, not even a tier 3, zero! Nada! no one wants to play with a class that offers little cc and no burst? (I HAVEN'T PLAYED IN 2 MONTHS! I MAY BE EXAGGERATING)
3- I'm kinda tired, not gonna add anything else (proceeds to add final thoughts anyway), im a filthy casual at best that just likes to spam 3v3 ques, I normally play around duelist range with guildies and enjoy it, but the class is just so boring and seems to be an afterthought with the devs with almost zero changes in sight... #FDKs matter... Please consider giving us 2H frost back? Obliterate to actually do damage instead of a wet noodle crit? Something? Anything? Just let us know that you aknowledge we're complete ass and we may be content then.