Playing through DB, I'm impressed at how refreshingly different it is from Skyrim. Perhaps it is only because it is a return to Morrowind (the soundtrack alone makes it worth the purchase) but it seems like it's ticking all the right boxes.
1. Fewer, more intricate dungeons.
2. Unique items make exploring interesting even at higher levels.
3. Excellent writing and quests.
4. V A R I E T Y

I wonder if this is what we can expect from the future of Beth or if it is only "DLC are always more fun than the original game because we've already played the original game".
I like fighting unique monsters - things that are unique to the game, not simply bears and zombies (Draugr) etc. I haven't finished the game yet but I'm looking forward to it...

Definitely!

Everyone loves and praises and talks about the Dawnguard DLC, but I think it's the Dragonborn DLC that really shines. Despite everything people hate about Skyrim, Bethesda really shows its qualities in Dragonborn. The locations, the NPCs, the unique items... everything! Better adventures to be had than on mainland Skyrim for sure!

It's Dragonborn alone that makes me really hopeful for TES VI

I haven't played any of the DLC's before. Since beginning it, I agree with both the above posts. Dragonborn has some beautiful artwork and music. Makes me wish for a PS4 and ESO!

I never played Morrowind but really enjoyed Dragonborn and Solstheim. There are some really, really great additions to the game, no matter what type of build you're playing (poison rune and virtual dagger spells, chaos enchantment, Dragon Aspect shout). Sometimes, I've played with a single focus (helping/serving Neloth), and other times, I've played with a broader focus (collecting Black Books or Dragon Priest masks). Either way, it's a fun change of pace from Skyrim. The only caveat is that Solstheim is pretty dangerous, you need to get some skills and attributes beefed up in Skyrim before heading over.

Dangerous is a understatement. Hell even the netch does some serious damage per hit.

Too true - but I've never played it with a difficulty setting below Master. Maybe on the lower settings, it's more 'hospitable'.

If you don't feel like dropping the difficulty setting, I found that doing the Dawnguard quests to the point where you can summon Arvak is very helpful. There are no horses on Solstheim so being able to summon your own gives you a much better chance to run away safely. Of course, once you get that far in the Dawnguard questline, you're no longer so squishy...

Good stuff, though, no matter how you do it. Challenging, engaging, exciting, rewarding...

Edit: postponing the main quest in Skyrim helps make Solstheim a little less dangerous. If not, dragons show up....