I got my Blood DK up to Mythic+ gear level and I enjoyed it a lot. For all the kvetching about Blood being a lot more simplistic and not having the same level of finesse and control, it's actually not true if you get into the new talents and really pick apart how they work. The amount that you can heal yourself if you use all your cooldowns is startling.
Yea I actually quite like blood DK defensively, I think it has a lot going for it and people don't give it enough credit. My personal issues with it are mobility and offensives. Mobility is the big tough one here, as a tank I hate when people are waiting for me to get to the next pack, it is the biggest reason I stopped playing my pally tank and from all accounts DK is even less mobile than prot pal. Would be less of an issue if M+ wasn't so "gotta go fast, beat the timer" based. Maybe a little better in 7.2.5 with the changes but still.
Damage/offensive tradeoffs is another issue I have, though it isn't that bad. Aside from just using DRW occasionally, you don't really have any offensive CDs or defense->offense tradeoffs. Even offensively you still want to use marrowrend to 5 stacks (for DS cost reduction), use Heart Strike otherwise, and Death Strike to burn RP, exactly the same as your max survivability rotation, maybe with less thought to timing DS uses. Maybe you could take Bonestorm but that's pretty much the limit for DPS. Pally, War, Druid, and DH all have very obvious tradeoffs to do more DPS (druid getting a better one in 7.2.5), not so sure about BrM but they probably do with Blackout Combo.
None of this is really that bad, though I kind of made a big post about it. There's just so little time to play alts this expansion that I wanna be really sure when I pick one. I guess it also bears mentioning that I play almost always with a really solid healer, and basically only do M+ and no raiding, so how much I need to optimize defensives vs a raid tank is probably less, with more emphasis on offensives to make runs faster.
