I don't
hate them, but I
do dislike them - mainly because they "come out of nowhere" and just end the game, often with little regard for the existing game state.
Now, they don't
actually come out of nowhere, but compared with a lot of other things they do. Combat presence is pretty much the other extreme - you can see someone has one creature, two creatures, etc, they're building up slowly, and you have a reasonable guess at how much they will be putting out next turn and how "close" you are to death, bearing in mind there may be pump spells, combat tricks, haste, etc. If, however, you have two combo cards in your deck, it's more about how many cards you've drawn which is a pretty statistical thing (and, admittedly, whether you've tutored). You can have nothing for the whole game and then bam!
There's an addendum here which is system mastery. If someone drops a
Grindstone, a player with a high skill level but low knowledge level might look at that and go, eh, that's pretty useless. Then they drop a
Painter's Servant and it's game over. Same with
Leyline of the Void or whatever. As a player, you have to know the combo potential of things, and it's not at all forgiving; if you get it wrong, you just lose. I just don't
consider that great game design, honestly.
Interestingly, my Acererak, the Archlich deck can "go infinite" but it doesn't work like this. It uses cost reduction pieces to be able to storm of with Acererak so whilst there is an element of "Oh, I dropped K'rrik, now I win!", it's rather dependent upon the board state. People can see it coming, or should be able to; if I have
Bontu's Monument out and cast Acererak ten times one turn, it should be pretty clear what's going to happen next turn. It's not really a combo deck (it's not trying to be, and anyway if it works people tend to die before it actually goes infinite), I just think it's interesting that it's a combo you can sort of build towards and which feels a lot more like a combat board state, rather than being all-or-nothing type of combo. (I think I have one with servos which is similar, actually)
The other reason I dislike them is that I find them boring. I
consider myself a Johnny; I like cool interactions between cards. Actually coming up with combos is quite fun, in fact. When you drop them, though, the interactions usually don't really matter. Except in some fringe cases, these cards may as well say things like "if you control card X, you win the game"... and that's, well, I just find it exceedingly bland.