Sword & Sorcery Immortal Souls is a fantasy adventure and dungeon crawler that was originally a kickstarter release in 2017, and subsequently has been released retail via a main core set and many expansions. It is a scenario based co-operative campaign game, where each quest mission is laid out up front, but there is a secret scripted book which is trigged by events on the boards. There will be random elements in terms of enemies appearing from a pool selected for each mission, and choices to be made which may affect how the story develops. 
In terms of production this is a great quality game, with models ranging from the excellent purple bosses to the more reasonably good enemy groups, but where some weapons can be a little soft and thin. Hero models have good poses, and enemies come in three colours (green, blue, red) which each have different abilities and responses, which increases gameplay variety and the difficulty level to fight them. The tiles are fantastic, thick cardboard and double sided with lovely detail and artwork, and with easy line of sight rules, they are some of best ground tiles in any adventure game. The kickstarter edition has had thick hero cards which are so good, much nicer than the thinner retail ones.
The rule and storybook are well done, the quality is very nice, there is an index, and whilst there seems a lot of rules to digest, they make sense and are easy enough to understand if you take time to read the book first. It does take more learning than many other dungeon crawlers, but this also makes a deeper game once the initial learning curve is over, and the prologue scenario is relatively straightforward to get you started. The storybook approach is also great and builds a very engaging campaign. There are loads of cards for skills and items and it will take time to digest all the various options, and there are many different tokens in the game. 
Gameplay is of course the key to a sustainable game, and there are definitely more little rules around as you have to remember the various enemy triggers, however the built in intelligence of monsters exceeds other games in this genre, and as such they do feel more alive, as you cannot anticipate every move. The dice are great, ten sided with symbols that trigger extra damage or abilities, they are some of the best around and like the Descent dice mechanisms are fun and interesting to use.
Heroes will spend soulpoints to strengthen and improve their skills as they progress, gaining new equipment and powers. Of particular note is that heroes can be played as either lawful or chaotic nature, which also changes their skills pool, which is quite unique. There is a real feeling of exploration and character development in this game, and your characters do not get fully killed off, but can be resurrected using soul points, keeping everyone engaged and playing throughout.
In overall terms, despite some extra complexity, if one player perseveres and learns it well, then this game is a really rewarding experience and provides one of the best adventure story experiences around. This borders on being classed both as an adventure and as a dungeon crawler and therefore competes in this genre, with a little more story, extra depth and greater monster intelligence.
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Expansions
If you bought the kickstarter edition then this will have simplified your need to buy many of the other expansions which are overviewed below (my additions highlighted green = own, blue = part owned, red = not purchased) :
Arcane Portal
This is a side quest expansion which branches off the original core box and uses the level 4 cap of the act one of the main game. You progress towards Thunder Mountain and encounter new enemies such as cultists, nightwalkers, efreet and a hellspawn boss along with new tiles and treasures to find. Whilst it is optional to the campaign, it remains an essential addition to enhance your original game content and experience at lower levels.
Darkness Falls
The story continues into act two with darkness covering the land, as you face the undead skeletons, deathknights, succubi, vampires and werewolves. More tiles and treasure cards and an undead liche boss develop the story and difficulty to the next level. This is a follow on set to the core and arcane portal and if you only buy one extra box then this should be the one if you want to progress past level 4.
Vastaryous Lair
A final boss showdown for experienced heroes from the original Immortal Souls campaign who completed acts one and two. A fabulous monster expansion box as you visit Black Queen Island to take on orcs, drakonic guards and the huge hydra. An excellent expansion.
Hero Character Packs
With Immortal Souls, there are nine hero add on packs you can expand into, each with their own skills card decks and models. It is unlikely you will need all of these, given you already have 5 characters in the main box, so selecting the ones you most like the look of is likely the best option. They include two that have slightly more content – Samyria the Druid who can shapeshift into bear form, Onamar the Necromancer who can summon entities to aid him, then a number of single model heroes Ryld the Blademaster, Skeld the Berserker, Volkor the Dragonheart, Kroghan the Barbarian, Morrigan Demon Huntress, Victoria the Pirate, Tristan Standard Bearer.
Component Upgrades
These are more about how the game looks and feels, there are a lot of options from plastic doors and chests, metal coins, extra dice, soul hero form models for alternative look or painting, plus some kickstarter exclusive card holders, draw bag and my favourite extra from the kickstarter is the thicker hero boards.
Ancient Chronicles
This is another whole core game set and story campaign released in 2021 and provides another fabulous adventure. It has an icy northlands setting with a new set of heroes and monsters all compatible with the original game and comes highly recommended and is a must have if you want more content. This adventure increased the difficulty level from the original but remains a great alternative or companion game.
Abysal Legends
Set sail for the final expansion adventure which is compatible with either core set, Immortal Soul or Ancient Chronicles, but does need acts one and two from one of the sets. You embark on a journey to reveal the mystery of a monastery, and find the sunken lands to fight more sea based creatures. Another great story it looks like, with four more heroes too.