I've just completed the Palace of Ice campaign (single player), so I thought I would give it a quick review.
Narratively, it's a direct sequel to the original Crown of the Magister campaign, with lots of returning NPCs as well as the party. It's very much the same style of generic fantasy. It feels a little flat, but I put that down to the lack of mo-capped cutscenes and professional voice actors that you find in more expensive games. It's really just there as an excuse to kick some demon butt anyway. It is livened up by some slightly meta comments on the differences between Solasta and licenced D&D, including the use of a spell that is not on the Solasta spell list but features in a certain D&D movie.
As with regular 5e, combat at this level is a case of throwing everything at the PCs and watching them mop the floor with it. Random encounter: ambushed by dragons? Only 5 dragons? Meh. Being a computer game, it does allow a lot more units in a fight than is practical in a tabletop game, and you will often find yourself with allies in the fight too. Which don't act too stupidly most of the time. Speaking of allies, you do have significant NPCs joining the party for a short span, but the game still does not allow you to access their inventories or level them up.
For DLC, this is a good length, a similar size to Lost Valley and the original campaign, but I did hit the level 16 level cap before the mid point, so there wasn't a great deal of progression in much of the adventure, aside from finding a few powerful magic weapons. Note that I didn't find any more powerful crafted weapons, not much use for crafting apart from making paralysis ammo, which is a bit too good.
The final conflict tries to up the difficulty by throwing a series of boss fights at you without letting you take a long rest. Suddenly I was glad I had dragged that warlock along for 16 levels! I guess the point is to use all those scrolls and potions you have been hording since the start of the game. Speaking of warlocks, I did find their high level spell list rather lacking in good choices, since you don't get slots you can's upcast. But that's 5e rulz.
