MS Paint Adventures is a web comic. It is not drawn with MS Paint.
The gimmick here is that the comic is an imitation of a LucasArts-style point-and-click adventure game in the vein of Day Of The Tentacle, with a text-based interface. Each update sees the protagonist confronted with a situation; a little text underneath the image explains what has happened and there is a flashing prompt, implictly requesting commands from the reader. (These commands are actually entered via the MSPA forums.) The author, Andrew Hussie, selects a command from the ones suggested and uses it as the basis for the next day's panel. The cycle continues and the "game" progresses, hopefully towards completion.
MS Paint Adventures is actually a broad umbrella under which a total of four separate adventures fall. In the first, Jailbreak, a man is trapped in a locked room with a key and a pumpkin and must escape. With the author constraining himself to always obey the first command submitted no matter what, the trapped dude swiftly discards the key, loses all trace of the pumpkin, knocks his jailer unconscious (from inside the jail, making escape impossible), pees out of the window, catches a harpoon through the chest and so on. It's initially hilarious, but the artwork is crude, the story quickly becomes puerile, tiresome and repetitive, and there is no real conclusion. I read all of Jailbreak in one sitting and, assuming that the rest of MSPA was in the same vein, left. This was a mistake.
Bard Quest has slightly improved visuals, though it still adheres to the largely black-and-white aliased MS Paint style established by Jailbreak. Bard Quest differs in the main by branching wildly. Many screens have three or four options beneath them, representing different suggestions given on that screen, and leading off in different directions-- mostly towards instant grisly death for the bard protagonist. This style of storytelling evidently proved difficult to maintain and confusing to follow and so, very soon, Bard Quest, too, was abandoned unfinished.
Problem Sleuth starts out more promisingly, with a cunning noir private detective named Problem Sleuth attempting to escape from his locked office. The story then proceeds to do nothing but skyrocket in scale and complexity, with the obstacle facing our hero (and his two plucky associates, Ace Dick and Pickle Inspector) rapidly mutating from "open your office's locked door" through "kill Mobster Kingpin" into "save the entire universe from complete annihilation". Unlike its predecessors, Problem Sleuth does have an ending. It concluded relatively recently. Is it a good ending? Yes. In fact, the entire comic is absolutely awesomely incredible.
Well, I could ramble on and on and on explaining all the cool things that happen over the course of this adventure, but I could never capture its essence with these mere clumsy words of mine. You would simply end up reading a series of inexplicable, unfunny in-jokes. Attempting to explain them could only subtract from the experience of watching it all unfold for yourself, which I implore you to do. Instead I'll explain why I think Problem Sleuth works so well.
A big part of it is that, like the other MS Paint Adventures, it is written almost entirely in the second person. "You are one of the top Problem Sleuths in the city," it begins. "Solicitations for your service are numerous in quantity. Compensation, adequate. It is a balmy summer evening. You are feeling particularly hard boiled tonight. What will you do?" This creates a connection between the reader and the characters whom you/I/we are ostensibly in control of. When the time comes for the final blow to be struck, it's you who commands the hero to strike, so it is very much you who strikes. Then there's the artwork, which begins at roughly Jailbreak level, but then continuously improves and increases in complexity even as the plot does the same. Detailed backdrops and murals are incorporated right from the beginning, but later this expands to cute animations illustrating actions the characters have taken, then to huge fractal landscapes, and finally to seriously impressive full colour widescreen attacks. There's a clear and really interesting style developing as the story progresses, and behind it there is an artist becoming increasingly competent with his tools, pushing himself to do better, which is extremely respectable. And because it's all done with GIFs, it never takes too long to load.
While the course of events is clearly being guided by the author at various points, it is also very clear just how much is owed to reader suggestions. Entire new gameplay mechanics are created from whole cloth because the author is smart enough to recognise a good idea when he sees one, grasp the possible story implications, and capitalise upon them. That is not a skillless task.
And there's the writing, which was deceptively crude in Jailbreak and Bard Quest but, again, becomes increasingly florid and colourful, glorying in ridiculous vocabulary and hard-boiled noir narration, without - and this is a really difficult trick - ever stopping being truly funny, even as the fate of the cosmos hangs in the balance. Plenty of web comics stumble when they make the Cerebus-style transition from street level gag-a-day strips to serious drama. Heck knows mine did. It's practically a trope.
Continuous improvement is a really gratifying thing to see in a web comic, mostly because it's so depressingly rare, but that is not the main reason why I appreciate MS Paint Adventures. I like it, because it's the first really compelling answer to the question, "How do you do comics on the web?" and the follow-up question "How about web 2.0?" Since the 1990s there has been a spectrum of responses to these questions, ranging from "just do a conventional four-panel gag-a-day strip like you'd see in a newspaper" through "target and entertain a profitable niche audience rather than aiming for universally appealing blandness" to "Infinite canvas! Micropayments! T-shirts! Prints! Bound collections! Premium content! MAGICAL ELVES!"
Infinite canvas is not how you do comics on the internet.
Animation! There's a newspaper comic strip, For Better Or For Worse, which (like anything worth speaking of these days) has a web site where you can view the strips online. Those online strips are GIFs. Why? Because it allows the characters in each otherwise absolutely static four-panel strip to blink unsettlingly.
Blink? MSPA annihilates those strips with a flaming sword and dramatic speed lines; with charm, lightning, gummy worms and atom bombs; with cheap, swiftly-created, lightweight (in terms of file size), sturdy, bright and glorious GIF animations.
User interaction! MSPA is user-driven. It shares a great deal with the tabletop role-playing game. The master is in ultimate charge of what happens in the story, but meanwhile the participants have no other purpose but to provide him with a continuous stream of inspiration. The result is an Andrew Hussie production, but it's really your creation. I define "Web 2.0" as "the internet with uploading as well as downloading"; websites where the user is able to contribute his or her own content as well as consuming what has already been put up there by other people. Everything2 is one of the earliest examples of these - there are also Wikipedia, Digg, Facebook, DeviantArt and so on. MS Paint Adventures is a web 2.0 comic. It makes full and confident use of comics-creation technologies that are only available online. It does not translate into any other medium.
The fourth and current MS Paint Adventure is entitled Homestuck. At the time of writing, it has only just begun. Expanding on Problem Sleuth, the author has taken to occasionally using Flash to provide smoother animation and occasional snippets of audio. So far, a few new game mechanics have appeared and a certain amount of atmosphere has been established. As for where it'll go next... well, one of your options is to relax, sit back and wait and see. The other...?