I made it half way through the game ,and couldn't stand its repetitive hack and slash game play any more! Its story is interesting but the gameplay falls flat on its face. If you must play it just rent it, i'm sure you'll know what I mean.
Okay I did think that Boktai had a great idea with the sun detector. I live in Michigan and it is cloudy four times out of five. Needless to say I am happy that they replaced the detector with an in game weather system. The top screen acts as a virtual sky while the bottom is where you will be playing the game.
Both characters are fun to play as and keeping them both charged is a lot of work with all the weather changes.
Overall the game plays like Castlevania would if it was set up in a Legend of zelda like game. There are almost no puzzles to speak of so if you want a straight up action RPG you can't ask to much more from this title.
I would ballpark the game at around 7-9 hours long depending on how much time you spend leveling up and upgrading you weapons. This game is a definite rent if not a purchase.
The game's pretty simple. You march around an area, killing guys with your sword, you level up, you get items, you fight bosses. The game is made interesting through a series of side-mechanics that sometimes work, sometimes don't.
The main quirk is the day/night mechanic. You play two characters, one uses lunar energy and one use solar energy. So at any given time, energy is readily available for one guy. Closely tied into that are the spirits. When you beat a boss you get a new elemental spirit. Enemies have affinities, so attacking them with the right element causes more damage (and all enemies come color-coded for your convenience). Some hidden areas are accessible only by using the right element.
Then there's the weather. Some puzzles are solvable by changing the climate, while some climates block the sun/moon and deprive you of a major energy source. You get new climates by, that's right, killing bosses.
There's also "weapon enhancement." Basically you collect scrap materials, and when you get enough you can bump your weapon's attack. You get a few different weapons in the game (guns for the sun guy, melee for the dark dude), but nothing really beats the sword. I could've done without the gun guy for a lot of the game.
The space battles are a way of making the touch screen not totally useless. You tap to shoot and drag to dodge. that's about it.
Throw in some items, a passable storyline, some cut-scenes and some decent voice work and you've got Lunar Knights. It's not the next Castlevania, but it's amusing enough.
Bottom line: it's an isometric hack-and-slash with some quirks. Worth the rent, might be worth the buy if it grabs you.