My first impressions from peaking through the full DLC playthrough is that the expansion is very intricately designed and has more great bosses- however it's missing something. Elden Ring had a pretty good story tying everything together with great characters, and a homebase in the roundtable hold. It had a huge sense of mystery too like the other FROMSOFT games. It also did stuff that was different than DS3 but it also re-used tons of assets.
In the expansion the Tarnished does not have a homebase it seems? And the only characters are a couple of NPCs that say a few sentences. There is almost no sign of previous friendly Elden characters.
Even though the game is impressive the whole franchise is starting to get routine again- I think we may be completely spoiled by what FROMSOFT has accomplished. The environmental design, while intricate are missing unifying themes (this was an issue in a lot of the Elden Ring maps too).
The more Souls-type games they create, the harder it'll be to create something new.
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The Messmir boss, which is highly touted by their marketing, is well made but not an epically replayable boss like Malenia Blade of Miquella.