Now I like your idea, but for me personally, it needs some work.
The font is terrible.
I'm sorry, I can't sugar coat it. It's barely legible looking at it on my computer, and the size and spacing you need to use to help people read it takes away from the overall look. There are a thousand better pixel based fonts that would suit this far better.
The system logo is far too big.
It's taking up a ton of real estate that would be better used for a games list. The user should have an idea what system they are on, so it doesn't need to be what your eyes are drawn too. Personally I would scrap it all together, or maybe split the rating, etc box into 2 smaller ones and put the logo there and then have the information a bit smaller.
Spacing/Consistency.
It seems kind of slapped together with a general idea of a layout, but no set spacing. The games list is closer to the top than the bottom as well it's further from the left side than the box other side of the screen. Visually it looks so much nicer when things are evenly spaced, and it's such an easy thing to master.
I'm attaching an image below of an old theme I had made like 3 or so years ago just as a suggestion as to how I would approach this. As you can see I create my full layout with guides and then build using them, even spacing between all the windows as well we as the edges.
Tiles
Use hard pixels since you're basing your design off of a pixel game. In both NES and SNES the tiles you've used are blurry, they should be crisp, as well the bricks in the NES should be the same size as the blocks. To be real picky I'd also say the bricks and blocks should be the same orientation since they are in the game, but maybe that's too much.
Again I like the style of the theme, but needs to be cleaned up a bit to really grab the interest, at least personally to me. I apologize for being an overly critical person, but when someone asks for criticism, I assume they want to hear more then "it looks great", when there are obvious flaws.
