As far Ratburn giving out too much homework, wasn't there one episode where Arthur was in over his head because Ratburn had given them something like 200,000 math problems?
Ratburn, to me, is, while obviously exaggerated, the perfect representation of a tough teacher that every kid faces, I'm sure there are kids out there who can look at Mr. Ratburn and say, "Oh, I had a teacher like that in such-and-such grade" (believe it or not, I can say I had a teacher like Mr. Pricejones in second grade). Speaking of which, "Return of the King" kind of puts Ratburn into a more human light, and for once, you actually feel sorry for him because of the pressure he's under to be just as good (and tough) a teacher as Mr. Pricejones.
Yes, he did seem like a strict teacher, at first, but that aspect of his character seemed to have been toned down after "Arthur and the Real Mr. Ratburn; Arthur's Spelling Trubble".
And, of course, there's also the humorous side to the character as well... admit it, how can you not crack up over, "Oh, so-and-so, I thought I'd drop by to give you the spring reading list and... OH! Are you having cake?!" "The Blizzard" was also funny for both him and Mr. Haney, where we see how the thought of school being shut down sends Ratburn into a tizzy, and how it's serious business to him, whereas Mr. Haney just wants to go home, to the point that when they're finally shoved out the next morning, he's on the verge of an emotional breakdown.