This is a MIXED review leaning towards negative in the last parts of the DLC.
+ Great level visuals. Fun to explore, new zombie cosmetic models. Custom zeds are interesting (if a bit annoying). Thankfully neither the Whipper nor the Clotter follow you into the base game as they dominate in small tight spots and the festival is much larger in most spots.
+ Fascinating story which helps you (kinda) understand what's going on in the main story. Possible sequel hook or future DLC hook.
+ Not terribly long. I loved Haus, but it did take awhile to plunder through (at a much lower level though).
- Whippers and later Clotters are fun to fight solo, but they tend to leap into unassociated teamfights and make stuff complicated. Whippers can deny your Fury mode so if you built on that, good waste of time. Their melee attacks require some of the finest dodging in the game (I don't run block, as I am playing Amy for my first playthrough). Clotters are all teleport spam, blood vomit, haymaker you into oblivion specials that are a chore to fight in groups of any makeup. And I hope you love that combo, because that's a huge part of what makes the last act of this DLC suck harder than a prostitute late on rent.
- The Dirge boss is a lesson of pain regarding every over the top difficulty spike you could imagine. You must do the orgone sphere minigame which the DLC worked you up to, with increasingly annoying and dangerous zed types who often ignore the sphere just to chase you, WHILE being chased by the Dirge during his invulnerable phase (he does seem to piss off when a sphere is nearly capped) but other than that he's up your ass the entire fight with his Boss Level versions of what makes Clotters annoying. Even at level 30 I was routinely being 1-2 shot by this guy, and my FPS was struggling to maintain 60 in the arena with the weird post processing effects and the rendering of what must be every single blood droplet in the world when he teleport spams (for reference, I get 110-120ish everywhere else. The game has that AMD flash card on load up and no DLSS which is a huge crime). You are quicksave starved during the progress of this fight, so you have to avoid his OHKOs via blood vomit or haymaker from hell (coupled with teleport spam) with plunging FPS (if you didn't go Team Red, no doubt. I have a 3080, not some piece of crap), and later they start chucking actual whippers, clotters and bursters at you with grenade bros during the final sphere. Although Steam forum bros will tell you they beat him in five seconds using just one hand while the other picked their nose, I'm adult enough to admit even with build changes, experimenting with throwables, and weapon types, it took me an hour to beat him. And I was not happy about it.
- Which dovetails into another issue. SoLA has the worst optimized areas in the game. The long draw distance of the main area with its 'heat wavy realism effect' seen almost nowhere else causes considerably FPS unsteadiness, which is exactly what helps Whippers spank me before I know they're there. The boss arena at Eclipse dipped to 31 at one point when I exploded like half of the explodable zombies while Dirge-Muh-Girge was teleport spamming. Unreal.
- The sidequest regarding the Amalgamation starts off very interesting and then has you fight four super clotters in the equivalent of a broom closet, on the dangerous Ground Zero Main Stage area which routinely spawns high level clotters OUTSIDE which will just follow you INSIDE if you don't kill them. So you die in the boss fight, respawn somewhere randomly outside, and all of the nonsense spawns around you. It's RNG if you can even get back in the boss arena to put up with the nonsense. What's worse is I know now what I need to do to win and I'm so tilted I'm writing this review and taking a break for the day. Nothing else in DI2 has made me do that.
The end-take is, SoLA has a lot of promise, and I think up until the Dirge fight it's well worth playing. But really, bring a tank or a buddy or two, because the endgame bosses are the worst example of fake difficulty I've seen in any Dead Island game. Or even Dying Light 1/2 for that matter.
EDIT: Upon reflection, it's possible my experience is because I've more or less hit level cap having done so many side quests and another DLC before getting to the story progression level which allows you to go back and finish SoLA. Because the content is not level locked but progression locked, and I'm a fanatic for doing optionals before carrying on, it's possible I've hit the scaling misery point some games have, where you get punished for being cap. And I was playing the squishy agile character as I did in DI1/Riptide.