Art:
The art in this comic is deliberately bad; that isn't a good thing. The fact that each of the last 400 pages has used copied and pasted images means that pieguy has never actually been able to improve on his artwork, 400 pages is more than enough to have significantly improved the artwork. I get that it's supposed to look bad and I do believe that art isn't as important in strip comics as it is in stories; but the art should always be presentable, Stickman and Cube is not.
As with a lot of MSpaint comics, the art hinders the jokes. Having a flat boring world, where characters can't express any emotions makes it hard for any of the jokes to hit. If Stickman and Cube could express emotions I think this comic would be much better. Look at xkcd, even though there is no actual faces in that comic, Randall Monroe does a good job of conveying emotion through body language. This comic makes frequent use of beat frames, this is usually a good technique but without conveying any emotions they don't do much.
Another issue with the art is that there is very little change in any shot types, this just makes things boring. As well as this, art can often be used as a tool for conveying humor, it never is here. For example, there's one comic where Stickman is in hell and he's told to stand in line, at this point we see a few people standing around, not really the big line that's implied. The comic could have had a different view of the line, showing it stretching off into the distance.
There are plenty of jokes in this comic that would have been funny had the art conveyed them properly; however, with the art how it is the jokes just seem bland as having bland art causes bland jokes.
Writing:
The humor in this comic can often be amusing, unfortunately that's not all the time. Too often does it seem to rely upon meta-jokes, which are really just a crutch. The fatal flaw in this comic is how often the butt of the joke is how lazy the author and bad the art is.
In all fairness the jokes have improved, I think there is less "how lazy is the artist, right guys? lol" jokes than their used to be. They're still there and as unfunny as ever, but it's nice to see things improving. I did rather like the 2010 election comics.
It's not like all the jokes are bad or anything, this comic certainly has its moments. Sadly, as I said earlier a lot of these moments are hurt by the art, other moments are just ruined by poor pacing which cause the jokes to fall flat without really any punch to it at all.
This is one example:
http://www.drunkduck.com/Stickman_and_Cube/index.php?p=774023
This is a comic I made up quickly with the same script but changed the pacing, and added facial expression and different shot types:
http://www.drunkduck.com/Thors_Thundershack/gfx/smandc.png
The same process can be done with a lot of the comics, improve the art, change the pacing a little, give them faces, and the comic's funnier. Adding stuff like this just makes the joke more sharp instead of them feeling flat the whole time.
On a lighter note, I really thought that the dialouge between Stickman and Cube was clever and funny. It just fell flat too often. Funny ideas are there, just not kickin' in right.
In conclusion:
It's not like this comic is terrible, it just needs improvement. It suffers from laziness more than anything. My honest advice for pieguy is to ditch MSpaint and start improving the art, no more copy/paste, and also stop making jokes about how bad the art is. I think pieguy should hone in on his main talent, writing dialogue and focus on that more. If pieguy wants his comic to be taken seriously and be well liked then its about time he put more effort into improving it.
Eventually, when your art's decent enough and your jokes are working, scrap Stickman and Cube and just start a new comic. One where the characters have absolutely no knowledge of being in a comic.
TL;DR
Stickman and Cube isn't good in its current state but would be with better art and less meta-humor.