I've played maybe 20-30 hidden object games to date (probably more), and I'd have to say Abyss is indeed one of the better ones out there, but has some flaws that really stuck with me as I played.
First of all, the game is beautiful. Although the detailed artwork is clearly inspired by the Bioshock series (and a lot of story elements), it looks great with a colorful palette and some imaginative locations. There are a lot of areas to explore, as well. The music is very nice and does a good job of setting the mood, but can get a bit repetitive after awhile.
For the game play, this is your standard IHOG/HOPA, basically adventure game lite with Hidden Object Scenes sprinkled in. As an adventure gamer myself, I always play on Expert to give me a bit of challenge and lengthen my game experience, but I found the game to be on the easy side overall. Not a horrible thing if you're looking for a relaxing evening, but I prefer my IHOGs to last longer than 4 hours on the hardest difficulty. Even the puzzles were fairly easy taking me only a few minutes to figure most out, and many needing only a few moves to complete. The most challenging part for me was going back and finding older Hidden Object Scenes that have reactivated; they don't sparkle in Expert, so it's basically a game of "let's click on everything" in the hopes the scene is indeed active again. I know this is pretty standard for Expert mode in most HOGs, but honestly, it's just an exercise in frustration, not added challenge. If the devs are reading this, putting in an option for sparkles on reactivated HOS's would be a much welcome addition in future games.
The Hidden Object Scenes themselves are well done, nicely drawn items without too much clutter, and have a nice range of difficulty, but none of the items were what I would consider unfairly hidden. And although I really enjoy HOS's, I know not everyone is a fan, so the option to play Dominos instead is a nice touch. The Dominos mini-game itself is fun, relaxing and mildly stimulating,
While the story took a lot of elements from Bioshock, it didn't resonate with me as much as some of Artifex Mundi's other games. I know HOG's aren't exactly a great source of deep, thought-provoking storytelling, but I felt like Abyss was flirting with some really interesting concepts, but those ideas kept getting derailed and neutered.
I think my biggest issue came down to the voice acting, though. Maybe I'm being a little more critical than I should be having come off of a couple of games that had absolutely amazing voice actors, but here...it's just awful. I wanted so badly to turn off the voices as every time any of the characters uttered something I couldn't help but cringe. If there is anything I would like to see in future HOGs it would be a toggle for the voices. Sometimes just reading and letting my mind fill in the blanks is better than being stuck with voices that are pulling me out of the experience.
That said, I did enjoy the game quite a bit and can see myself playing it again in the future. I certainly look forward to some of Artifex Mundi's other games making their way to Steam.