It's odd that the only review on this page is for a specific, not particularly memorable episode. Oh well, here goes...
The first thing to note about the AVGN is that he does not give particularly detailed reviews of the games he is playing. Typically, an episode will have him expanding on the game's background (particularly if it is licensed from another medium, which is often the case), playing through the game, encountering flaws, and then comparing those flaws to animal genitalia or faeces. It's a simple and very juvenile form of comedy, and it shouldn't be funny. But it is of course, thanks primarily to James Rolfe's commitment to the character's authenticity. By contrast, explaining the games roots is often played straight: it's almost as the Nerd feels the need to get the preamble out of the way before getting down to the bit people want to see.
Some episodes have more of a plot to them, and these tend to be the ones which James puts more effort into. These plot-driven episodes vary, but the most common pattern is for the Nerd to develop a conflict with a real-life version of a character in the video game he is reviewing. Expect their tension to grow progressively worse until by the end of the episode they are engaging in a no-holds-barred brawl - and I really mean no-holds-barred. Again, the laughs are not overly sophisticated, but my inner child never gets tired of watching Bugs Bunny loosening his bowels right over the Nerd's face.
It should also be mentioned that the visual effects in this show are awesome considering its shoestring budget, and that it is made almost entirely by one person. Both special and good old practical effects are very well done, although it must be said that these do not necessarily improve the show itself. Rather, they come across as self-indulgent, as Rolfe satisfying his own cinematographic urges - somewhat like Terry Gilliam, he's a filmmaker at heart who stumbled by accident into a massively successful comedy. It also seems like he feels the need to keep making the show bigger, when honestly, it's doing fine as it is. It's a review show - just snarking at the game's eight-bit follies is enough to keep me happy.
Overall, this isn't a highbrow show, but crucially, it revels in being a very good lowbrow one. Sometimes I question why I'm finding it funny, but that doesn't stop me watching.