As Machinima becomes more popular, the tools and options available increase, whether it be because of the use of a mod or actually added in by the Developers. Halo 3 is one of the most notable developer additions (with the Replay Feature and Stage alterations), and Brawl seems to be becoming one of the most Game Mod-based, from stages to movements.
The jump in quality from Garry's Mod to Source Filmmaker in terms of animation is pretty much day and night. Barring difference in tools, any animator who works hard and frequently enough on their craft will improve.
The G Mod Idiot Box has also improved in animation quality over time as DasBoSchitt started to incorporate stop-motion animation into his Gmod videos.
The art style of Neopets became more polished and refined over the years, giving them an overall "cuter" appearance and more dynamic poses. One oddball change is Bruce, which was originally represented by a picture of Bruce Forsyth (then a cartoon caricature of the same before entering its current penguin design). The color also improved greatly, going from generic gradients and flat colors to actual shading.
In Tokyo Magic Star, first the art looked rather simplistic and chibi-like, with lots of wobbling lines, but as the series continued it got more complicated and realistic, with straighter lines.
Popular video series ASDF Movie has probably one of the easiest to notice, even by comparing the first installment to the second.
The Awesome Series by Egoraptor. Go compare "Metal Gear Awesome" to, say, "Pokéawesome". Keep in mind Arin Hanson is completely self-taught.
AtheisticYouTuberDarkMatter2525's animations have undergone this. At first, his characters were drawn with black dots for eyes and squiggly black lines for mouths that moved when the characters spoke. Nowadays, they have regular, white and colored eyes and proper mouths with teeth and everything. The artwork in general is much more polished and refined, wih much more details and better shading compared to how it was in the early videos.
You. Are you a writer or an artist? Go compare the earliest work on your Tumblr, dA, Sheezy Art, FA, etc. to the most recent thing you've drawn or written. The more you study and work at your craft, the better you will be.
The Most Stupid Deaths In Super Mario 64 begins with Mario looking normal, but, starting in the fourth episode, Fleskhjerta (the creator) began to use gameshark codes on the game, making Mario and other things look different.
The art in Vaguely Recalling JoJo is mostly sloppy and consists of still pictures which shift frequently. However, the quality of drawings and animation noticeably improved over time(especially during Iggy's battle with Petshop).
Gamingandstuff 's sidebars: He went from no sidebars, to sidebars made with a mouse in paint and hand-made sidebars to photoshop sidebars with images taken from the internet
In the Edutainment show Geography Now, the infographics in the first episodes was crude, because its creator was all by himself doing the writing, directing and editing. After he managed to get help with some friends and then professional graphic designers, they looked progressively better and better.
The initial goal of Googlebrains was to be a Toontown Online channel in a similar vein to that of Quackity HQ. This is obvious in "TOONTOWN FAILURE (1)" and "Old YouTube be like...", which were some of his first videos.
Yellow Guy and Duck Guy had their puppets rebuilt between the first and the second video; Yellow Guy has a more defined body and a more noticeable jaw (in comparison to the first video where he was a Muppet-style handrod puppet) and Duck Guy received longer articulated legs for the sequel.
In the third video, the Yellow Guy was changed yet again by giving him white shoes and a noticeably shorter mullet.
Yellow Guy's hair was yet again changed in the fourth video, giving him hair that is strikingly similar to his appearance in the second video.