In various forums and articles, it is frequently mentioned that Homelands is one of the worst, if not the worst, Magic the Gathering expansions. Even on the main Wizards website, you will occasionally see this mentioned. Is there any canonical consensus as to what was wrong with the expansion?
It helps to look at the whole set in Gatherer and think about what you don't see.
Basically it's a set that's full of rather weak creatures and almost nothing else. Have fun turning Spectral Bears sideways!
Mark Rosewater described Homelands this way:
This reputation was further cemented when Wizards tried to "fix" Homelands' unpopularity by adding stupid rules forcing you to use Homelands cards to the first Pro Tour.
What I find surprising isn't so much that Homelands had all these problems but that the original Magic set (Alpha/Beta/Unlimited) largely didn't. Most of the design space of modern-day Magic can be traced directly to about 300 cards in ABU: direct damage, removal, countermagic, bounce, fast mana, mana ramp, card draw, card filtering, tutors, sweepers, tokens, reanimation, X-spells, even morph.
But, even if you use the core set or previous expansions will make up for them, I think the gaps in the set are still noteworthy as reflections of the designers' general unpreparedness and confusion: Why are there no real burn or removal in Homelands? Because the designers just couldn't seem to get their heads around the role of those things in a game of Magic. Instead you've got way too many narrow cards that try to answer strategies that were mostly too weak to need "answers" anyway.
Overall, it has the feel of someone taking their "kitchen table" dynamic and turning it into a set. I think that's a reflection of the set being designed by folks who weren't really plugged into the ways Magic had developed as a strategic game.
Even ignoring all the aforementioned reasons in the others answers, I would simplify saying that it's just not fun to play with.
I tried playing with my friend using only Homelands set cards and it was horrible. You couldn't do any interesting combination, no strategy. You feel powerless, impotent.
A lot of people (kids at the time) bought large quantities of Homelands boosters because they were cheaper than the alternative (Revised, fourth edition, Ice Age, Mirage), only to realise the cards were unplayable. People ended up hating the set.
First off, let's clarify; Homelands was "bad" in that it was a poorly designed set for the purposes of playing Magic. This is observable via the incredibly small pool of Homelands cards that have ever seen play in any Constructed format, ever. It was so bad that at the time of Homeland's release when the first Pro Tour was happening, Wizards instituted a rule that each deck had to contain at least five cards from every Standard-legal set in their decks, just so that new the Homelands cards would be showcased in Pro Tour decks.
As for why it was bad, the general consensus is that it was a set designed from a plot and story perspective, with not enough care given to gameplay and mechanics. A good history of the design is given in the reprinted article, Homelands: The Making of a Magic Expansion.
Overall, it just didn't do enough:
I'm tempted to mark this question as subjective, but I suppose we can try and look at it from a more objective "what makes magic work" and how you define "bad" viewpoint.
What makes an expansion bad? I can think of two things: how it contributes to the limited environment (drafts, sealed deck tournaments) and how it contributes to the constructed environment (standard, extended, vintage, etc.)
So let's take a look at commons to evaluate how limited for Homelands is like. Ugh. Overcosted, low power creatures, quite often with significant drawbacks or costs for minimal abilities. As just one example, compare Samite Alchemist to that staple of original Magic: Samite Healer.
Now, Samite Healer was never that great to begin with. Two mana for a 1/1 body in white, tap to prevent one damage. So if he's blocking alone, it's like getting 1/2 body for two mana. Of course you could use the healer on other creatures for fancy combat tricks. Still, its impact is fairly minimal.
For Samite Alchemist, you have to pay two more mana for to get a 0/2 body, and to prevent 4 damage (not an insignificant amount, I concede) not only do you have to have two untapped plains to save it, but you also have to give up the use of that creature for next turn. If someone decides to use direct damage before your attack, to save it you must give up two turns of it not attacking.
I'll leave it as an exercise for the reader to go through those commons and see how weak they all are. If I remember correctly, the only common to see significant constructed play was Serrated Arrows.
The Uncommons and Rares were also similarly weak and overcosted. The uncommon filter lands were terrible. Here is a list of Homeland cards on Gatherer rated 4 or better. Count 'em. Seven. Not sure how Didgeridoo snuck in there but I suppose it would work well with Changelings. :)
How do you judge an expansion as bad objectively? Well I suppose by the value of the cards, when it came out and over time. I remember when Homelands came out at the height of Magic's initial wave of popularity, and if I remember correctly, its print run quite outstripped demand. This also contributes to it being perceived as the worst expansion, as none of the cards really got to be worth much due to overprinting and low demand.