The Cave was a big disappointment for me. I used to consider myself a Double Fine fan, considering practically every DF title to be an instant purchase. However, I consider their more recent releases to be of much lower quality than I would expect from a developer I admired so. The Cave was the first of these.
First off, as a puzzle platformer, most of the puzzles in the game aren't particularly challenging or interesting, often consisting of a simple "find key, open door." Some puzzle mechanics are fun, such as the Time Traveller's ability to alter events in the past to change a level's layout in the future. Mechanics such as these aren't very common, as many of the puzzles are generic so that any character can complete them, likely to avoid conflicts in your party composition.
Every character has their own backstory which covers how or why they arrived at the titular Cave, but after going through the first couple of characters' levels, you'll notice the common theme pretty quickly and the story exploration becomes uninteresting. It almost feels like an attempt to make "another Psychonauts" by the nature of its writing, with The Cave's backstory exploration echoing similarly to the repressed memories in Psychonauts. However, many may find The Cave's characterization extremely lacking in comparison. Its humor is there but it lacks the quality writing underneath which made other DF titles work so well.
The Cave tops off its first (very short, no more than 4-5 hour) playthrough with a picture montage (yet again reminiscent of the repressed memories in Psychonauts) and a text notification informing you that you have beaten The Cave, rather than any sort of proper ending. The Cave encourages the player to go through the game at least three times to unveil every character's backstory, with the game not "actually" being beaten until then. Due to the repetition of solving many of the same puzzles across each playthrough, I was not interested in finishing the game a second time. The writing wasn't even interesting enough to convince me to power through the repetition of doing them again.
All in all, despite its many weak points, The Cave has a few interesting puzzle mechanics that make it worth playing, especially if it can be grabbed for 75% off or more. Unless it's a title you are very interested in, however, I'd avoid it altogether.