This game is absolutely awesome. Oniken is a 2D run and sword action game. The controls are simple, attack, jump, duck, berserk and up + attack to throw a grenade. It is all so nice. The attack distance is good and can be boosted with power ups you find. You can hang from things. This game really goes the extra mile to make you think you're playing something for the original Nintendo, while most other games going for the nostalgia feel don't have actual 8 bit graphics and music. I feel such a buzz playing this game unlike other 'retro-ish' games that miss the mark with modernized graphics and sound.
The cut scenes are nice to look at, but the real fun of the game is the game play and the enemy variety. You'll see a lot of enemies and tackle them in different ways. For modern gamers the game might be seen as difficult due to the fact if you die, you restart the section of the level. Die at a boss, restart that entire section. You'll get better! Lose all of your lives and you'll have to restart the level. Each level mainly consists of 3 sections, each with a mini boss of some sort. Since the save file allows you to just jump to a level, if I die on the first section of a level, I just go back to the menu and warp to the level I was on. Kinda makes lives on the first section of each level pointless. You have a hefty health bar like Mega Man, so the game is pretty forgiving. Pits are of course instant death.
The level variety is a mixed bag. Some levels are just bluntly walk to the right, others make you scale to the top and still others put you in a jet ski with a scrolling screen. There are a few sections that feel open where you're free to make your own path, which feels good. Some levels are needlessly difficult with a lot of action happening, but if your a veteran of old Nintendo games, you should be used to it. If not, then make an angry video about it.
There isn't that much replayability for the game, there are a few hidden items, one per level, and there are achievements for beating a level without dying. The game saves your high score for each level, but really, once you've beaten the game, there's no reason to come back to it.
Again, this is an awesome game well worth $10, it is so awesome that I'd buy any other game this studio comes out with. They hit the nail on the head. If you aren't into old school Nintendo games, avoid it.