This is what happens when Hideo Kojima mixes MGS, Castlevania, and Zelda into a big pot and cooks up a masterpiece.
The basis of the game is that you are the new Solar Boy, Django. Your original intent is to take revenge for your father by destroying the count, but then you and the sun spirit Otenko get thrown into a quest to save the whole world from becoming undead puppets of the immortals. Armed with only your father's Gun Del Sol, you have to triumph over several dungeons crawling with undead and the lairs of the immortals plotting against you, all the while dealing with your rival, the mysterious Django-look-alike, Sabata.
This game features a solar sensor that has multiple effects on the game. The most basic of its uses are for determining how fast you can recharge the battery in the Gun Del Sol. If you have strong enough sunlight, the battery virtually won't drain at all, but conversely if you have no sun light you can't recharge without the use of a solar station or items. More complex features are that the sun affects various things in dungeons, like sunlight coming through sky lights and weather or not water, which gives away your location if stepped in, is on the ground. The tool used to defeat immortals, the Pile Driver, requries at least one bar of light on the solar gauge, so playing this game from start to end in one sitting is not very plausible unless you start at sunrise and don't stop playing for anything, but that's not a good idea as your gun will over heat if it receives too much sunlight and you won't be able to fire it. The game also features a time function which determines where you find certain enemies and also at night time you can see the solar bamboo shoots (they're still there in the day time, you just can't see them) which most of the time contain solar bugs or life bugs, but some times contain dark bugs (and always contain dark bugs if you fail to pay your loans off...). Other than that, this game plays very similar to Metal Gear Solid or any other stealth game, where you are rewarded for completing the game undetected and only killing when its necesarry. It also features a wide array of puzzles to be completed in order to progress, serveral are similar to what you might find in a Zelda game, but most are fairly original.
I thoroughly enjoyed this game, and there's still plenty more to do once you beat the game and I would play it through again if I didn't have so many games I still need to beat. I'd recommend this game to anyone