It's fun to see a throwback to the Ghostwalk campaign setting from the D&D 3.5 era. I've always appreciated options that allow a player to continue playing the same PC, even after that character died. The Eidolon provides a solution to that challenge. There are seven different paths, and your Eidolon will be able to choose three of them by the time they reach 6th level. That's 35 different possibilities! Combined with the feats and spells offered in this supplement, and that's a whole lot of content for your back-from-the-dead PC.

I appreciated the flavor text scattered throughout the book. It never mentions the Ghostwalk setting, but references to manifest wards and ectoplasm draw enough flavor from the setting, while making it available for any campaign where the tone is a good fit. Not every setting is going to feel right with physically manifest ghosts showing up. But I suspect many would benefit from a character where this is essentially their One Unique Thing. The setting doesn't have to be a haven for Eidolons if your PC is the only one (which is possible even without a manifest ward, thanks to soul anchors).

I'm giving this book four stars rather than five for a couple reasons. First, the text could use another pass from a copy editor. There are some extra words and other small punctuation or grammar issues that made it into the final product. It's by no means widespread enough to make it hard to read, but I'm the kind of person who notices these things, and it draws me momentarily out of whatever I'm reading.

Second, there are a couple mechanical choices built into the class that could be problematic. At first level, an Eidolon can choose the Path of the Corruptor and gain 1d6 additional damage to all melee weapon attacks. Unlike the rogue's Sneak Attack, the Eidolon doesn't need to have advantage, there's no once-per-turn limit, and there's no limitation on the weapon type. That's just flat-out better than Sneak Attack. At 9th level, this increases to 2d6 additional damage, which is amazing. Path of the Traveller grants a fly speed at 1st level. It's slow (just 5 feet), but any flight at all can be game-changing. So there are some potential balance issues here, and they're going to entice players to want to "dip" into Eidolon by dying. That brings me to the means by which this class is used. You must have a level in another class before your character dies and becomes an Eidolon. This leads to the unusual requirement that you need to strip your character of their previous level before applying the first level of Ghostwalker. Unless you die at 1st level, you'll need to go through your character sheet and remove all features that came from at least one of your levels. It doesn't specify which class, if you've already multiclassed up to that point. It's the kind of thing that could lead to players having to flip through books to figure out how to turn back the clock on their PC.

If your players aren't too concerned about balance, then this is a very flavorful class, and packs a lot of options that appear fun to play. I'd absolutely consider playing a Ghostwalker in my home game, where we're more focused on RP than on PC balance.