Doom loads heavily on the GM's side for opportunity, gameplay, and downright power. As a player (Marine), you will have a number of lives. You will have weapons with excruciatingly limited ammo, and a power-up or two to get you through these deadly dungeons. In the turn sequence, you and your fellow marines all move through the dungeon, often fleeing monsters and trying to escape death (in order to save your lives for later). You have few choices as a marine, all of them requiring basic tactics like movement, attack, defense, and, well, trying to escape death. Your "turn" as a marine will be over shortly, and you will be left wishing you had more to do, and feeling impotent to escape impending, uh, doom.
As the GM, you'll have a ton of cards (options) at your disposal. Each room of the dungeon you introduce to your players will invariable spawn out a number of monsters for you to control, and you'll be encouraged to use cards and use them often. Some of the cards spawn monsters and some hinder the marines. Some of the cards are so sadistic, and leave marines with even less power and options in the game. So in a typical GM turn you'll make multiple tactical decisions (controlling monsters by moving and attacking and playing instant cards) and strategic decisions (planning cards for further down the line, saving cards and attempting to influence marine movement using tactics, etc.). Your turn doesn't end there, however, because as the GM you also will have instant cards that you can play during marines turns to render them totally powerless, and if each piece of the gameboard that is exposed isn't filled with enough traps, your cards will have trap-like effects as well.
On the positive side, there is a Call of Cthulhu RPG element to this. The probability of victory is stacked heavily on the side of the Elder Gods, not the players (investigators), but as a GM you can still urge and help your investigators along, even rooting for them to emerge victorious (or at least alive) from their insanity-provoking adventures. If you are a sadistic GM who gets his jones by quickly (and sometimes humorously) dispatching with your investigators in CoC, you probably haven't planned a lengthy, involved, character-oriented campaign anyway, and are more interested in having a laugh and seeing just how powerful and dangerous the world of Lovecraft's really is.
Similarly, in Doom, you certainly have the ability to give your players a rough and tumble ride but to root for them. You can prep out some major accident cards, some instant cards that demoralize them but you can also give them the leeway to feel like they've got a chance, and if you're really good and really care about providing a fun game, you'll actually help them get far enough and feel competent enough to enjoy the game, even if you want to "win" by taking all of their lives. But if you're the sadistic type of GM, the kind who loves to kill his players off one by one with no mercy, you're going to have a little too much fun, and also make the game completely un-fun for the marines. Whereas in Cthulhu the environment is rich, the good humor enlivening, and the unspoken understanding of cosmological insignificance part of the fun, in Doom, the marines already have little to no choice--they are not only cosmologically insignificant, but they are essentially imbeciles. They can't hide, they can't think. They are pawns and their lives are of little value. All they can do is run, run, run, and maybe kill a monster or two, which is already not too fun. The sadistic GM, then, can ruin a game by only adding far too heavily to the challenge. They can make the marines lose the game by killing them one after the other, which is fine. What is not fine is that they can suck the small amount of fun out of the game by torturing players with over-powered instant cards and swarms of monsters. They can make players feel completely powerless and without choice--two of the worst things about bad board games.
Now, this can be incredibly fun for the GM. There is no doubt that a full-on power trip can be a blast, and that knocking off players' lives one after the other can be a lot of fun. It can even be helpful if you announce in the beginning of the game, "I will take no prisoners. Good luck," or something to that terrifying effect, and then dump monsters into a room. But there are usually going to be one or two more players on the side of good, so you have a game which has an uneven power dynamic in which the party in the minority has a ton of power, and everyone else playing is powerless. I know I'm beating a dead horse, but I want to make it clear: this unbalance is not just unbalanced. It is broken, and a nasty GM can break it more.
Another final, ghastly thing that ruins Doom. You have lives. I mentioned above that each marines were powerless buffoons. Well, also, marine players lose lives like in Mario Brothers. While this adds to the video-gamey, hack/slash/and mostly run-mechanics of the game, it reduces even more the feeling of atmosphere. This makes your already powerless marines feel so disposable that it is very difficult to get that roleplay element that enriches similar odds-are-against us games like Call of Cthulhu and Arkham Horror.