Just coming to ArcadePark.net as a new visitor, first impressions are great. It looks shiny, clean and colorful. Darker blocks against a light blue background work very well, especially with nice matching category images. It would help to link those images to the category as well though, not just the text link.
There could be some improvements on the category pages, however. White text on a blue background might look better than black. I would also suggest making category images of uniform size and floating to the left of the text rather than above, in order to look cleaner. And smaller next and previous arrows beneath the listings, perhaps using images instead of text arrows.

On the actual game pages everything is clearly separated, the description, embed code, game review form etc., but it could use some fine tuning. For example, the "full screen" and "add to favorites" links positioning could be improved by raising them and making them centered.
I also notice that the site doesn't have a distinct footer so the text at the bottom seems kind of lonely in the sea of blues.
And finally, I would also suggest slightly increasing the font size.
In short, great first impressions, but could still use some improvements.
Design rating: 7/10
Focus:
In addition to the obvious site name the welcome block offers a clear, concise yet informative description of the site and what it has to offer so there's no chance in hell someone wont figure out what this site is about.
Sidebars are what the user might come to expect, top 10 and newest games, some statistics and top 10 players. However it is not clear how do players become "top 10". Is it by the overall sum of scores, number of times played or something else? It's a very minor notice, but just to make it perfect, something to perhaps look into.
It is also not entirely clear what is gained by actually registering to the site.
Focus rating: 9/10
Content:
The number of games available isn't too high yet compared to the amount of categories, which becomes fairly noticeable when browsing categories, but this is understandable if the site is new. At least no category is empty so users are guaranteed to find something fun in each. And it's very easy to start playing.
Content rating: 9/10
It is one of the better arcade gaming sites I've seen, at least judging from the first impressions. If it continues like that and especially after the suggested improvements, it may have what it takes to be a respectable contender. I'm actually tempted to bookmark it myself.