Season 1, including the pilots (2004-2006) was a little shoddy, but they at least had excuses as for why. For the pilots, James did those as a joke about taking games (especially old ones) way too seriously, and he didn't expect to do more beyond those. For Season 1 in general, James was only able to do episodes on his free time (and yes, he actually could use "muh time" as an excuse back then) since he had a real life job. All of this meant the episodes of Season 1 were extremely basic, although James going freelance later on meant he would have more time to do Nerd episodes. Excluding the pilots, the best episode (IMO from here onwards) was TMNT (the episode that made AVGN popular), the worst episode was Master Chu and the Drunkard Hu (which "guest starred" a particular pickle with feces on its head, that episode is just a little unbearable to watch because of it)
Season 2 [2007-2008] saw an increase and quality, and in turn, more episodes that were good and rewatchable. In addition, James began a contract with GameTrailers, in association with ScrewAttack, to post new episodes on their website. In turn, these AVGN episodes wouldn't be published to YouTube first, instead they were uploaded there between 2008 and 2009. The season itself is beloved for probably being James's creative peak for the show, featuring innumerable camera angles for many episodes (see that cherrypicked meme for reference), and episodes overall being far more experimental than those that came after the season. The best episode was Spider-Man (guest starring Kyle Justin, the guitar guy, as the titular character), the worst episode was the Legend of Zelda Timeline (as James himself puts it, he wasn't even "furious" in the episode, and it was a holdover from Season 1)
Season 3 (2008-2009; published on YouTube between 2009 and 2010) would see the show move from the apartment that James had been living in since the previous season to the current "Nerd Room" in the basement of his new house. There was far more room in the basement than in his house, and in turn, gave James much more opportunities for episodes. The best episode was NES Accessories (which happens to be the most viewed AVGN episode on YouTube as of this writing), the worst episode was Deadly Towers (though I don't see it as a bad episode, it was pretty creative to be honest, it did kind of foreshadow how try hard James would be with the scripts he would be given in ten years' time)
Season 4 (2009-2010; published on YouTube between 2010 and 2011) was effectively peak AVGN. A healthy variety of, as James puts it, "basic" episodes (e.g. Super Pitfall, Plumbers Don't Wear Ties) and "epic" episodes (e.g. Crazy Castle, Ninja Gaiden) were present in this season. The season was also the most memeable, with clips being utilized from episodes like Transformers ("That's right, we're gonna cheat!") and Pong Consoles (the scene where the Nerd shoots at the TV) for comedic effect. The best episodes were his retrospectives of Castlevania games (personally, it helped me get into Castlevania more). The worst episode was X-Men (it's actually a fairly decent episode, but was a little boring in my opinion).
Season 5 (2010-2011; published on YouTube between 2011 and 2012) saw the show reach 100 episodes, celebrating that milestone by reviewing ROB the Robot and its games. James had burnt himself out by this time due to his two episode per month schedule, and would thus scale down this schedule to about one episode a month. The show started showing some decline in quality, but was still a very decent season,. The best episodes were the twofer of Action 52 and Cheetahmen (they felt like they were the last Golden Age AVGN episodes in a way). The worst episode was How the Nerd Stole Christmas (its not unwatchable, but its way too gimmicky for its own good)