Yumemi Mystery Mansion (Mega CD)

I remember when the Mega CD first came out in Europe, this game was previewed a lot in magazines. I assume it got so much attention because of the prerendered CG graphics, and the fact that there wasn't anything else like it on the SEGA consoles at that time. Since then it seems to have been forgotten by history. I'd even forgotten about it until recently, when I played it for the first time.
It's an adventure game set in a mansion, that you entered following your sister, who in turn was following a butterfly. You wander about the mansion, seeing it all in first person perspective, and although everything is prerendered, it still moves pretty smoothly, and though the graphics are low-res and very grainy, that only adds to the atmosphere. Atmosphere is by far the game's strongest point. Even though there are no enemies, and there are only (as far as I can tell) two ways to get game over, the game still manages to be creepy just by the strength of the atmosphere it creates, and the bizarre premise in general. The only other characters you meet in the mansion are talking blue butterflies, who are the souls of people trapped in the mansion by its owner, the unseen malefactor referred to as The Hunter. Your objective is to find your sister and get out of the mansion before midnight, at which point you and your sister will join the other residents as butterflies, trapped in the mansion forever.
As there are no enemies in the game, the only things obstructing your escape are the various puzzles in the mansion. Most of the puzzles being of the "find the item/key and use in the right place", made even worse by the fact that you're often given no indication as to where the items will be, and on top of that, some items can be seen from the start of the game, but can only be picked up later in the game when they're actually needed, with no indication that this is the case. I'm slightly ashamed to say that I actually had to resort to consulting gameFAQs for the final puzzle.
Despite all the faults this game has, I still say it's worth playing for the creepy dreamlike atmosphere, especially if you're interested in horror in videogames. It's only an hour or so long, so it's not going to waste too much of your time. The fact that it's so short, coupled with the general lack of gameplay and the fancy graphics does make it seem more like a tech demo than an actual game. It probably would have been more fondly remembered had it been a pack-in with the console than a full price stand alone purchase.
(This game is also known as "Mansion of Hidden Souls")