Looking at a Random Card: Terrain Generator
(What am I doing here? Read here!)
Terrain Generator: Ah, a land! Now I have at least one card from each of the major card types (planeswalker and tribal are still missing… okay, and artifact did only come in conjunction with creature so far).
Terrain Generator is such a card which looks really unexciting on first glance. Then, you start to think about its possibilities and it becomes suddenly somehow interesting. After a while, though, you realize it is actually every bit as unexciting as it seemed at first. Its obvious purpose is to allow you to put extra lands on the battlefield, but at way to steep a cost: You need to already have 3 mana available, which means that its main use will be to get a 4th land out on turn three. That’s not much of an advantage, since you effectively skip your third turn to do so, unless you have at least another land on turn five (if not, you could just lay that 4th land now, with little loss). That is quite a minor advantage to a card which provides you with only colorless mana, and at the same time, requires you to use a good number of basic lands. Yes, it only takes a land slot, but usually, if you go for mana acceleration, you will have better options available – likely something which will give you 4 mana on your third turn, which is way more crucial than jumping to 5 mana on the fourth, or something which helps you to fix your colored mana at the same time instead of just offering colorless mana by itself.
The same is true if you build a deck which somehow reliably draws so many cards that it really wants to lay two lands on several turns (probably using Howling Mine and its ilk): You have better options (once again, artifact mana costing you two is just a way better deal, especially if you use stuff like Fellwar Stone or Mind Stone which effectively costs you only one mana, since these cards don’t enter the battlefield tapped). And that is, obviously, if you’re not playing Green, where you have access to a plethora of more useful effects.
But wait! Aren’t there cool tricks possible with putting lands on the battlefield at instant speed, and possibly on an opponent’s turn? Why yes – there’s landfall and… okay, mostly landfall. But isn’t that enough of an incentive to include the Generator in a landfall deck? No, it isn’t. Costing you effectively 3 mana and requiring you to have that land in hand makes it way too clumsy. You’ll just use fetchlands instead – even if you’re on the tightest budget, you can use 4 each of Terramorphic Expanse and Evolving Wilds (both costing next to nothing), giving you plenty of “instant” land effects on clearly better cards, and actually providing additional land drops (which Terrain Generator doesn’t – it just allows you to make them at different times).
Okay, but what if you want to design a cube? Wouldn’t it be nifty to put this nearly forgotten Nemesis uncommon in an environment with landfall? Well, that’s what I thought at first. Turns out I was wrong! See, the Generator is still clumsy – especially since landfall really is an aggressive mechanic encouraging you to spend your mana way more efficiently than on the Generator’s ability. Then there’s the competition of fetchlands again – they just play better in every way. The last straw, though, is the Generator’s incapability to put other lands than basic ones onto the battlefield – in contrast to, for example, Walking Atlas – because any environment featuring landfall wants some synergies with ETB effects like those from Teetering Peaks or Soaring Seacliff. Honestly, even if the Generator could be used to get you these effects at instant speed, I don’t think it would be worthwhile to include it in a cube, but without that most interesting trick, it just hasn’t anything going for it.
So, if it’s practically useless in constructed, and not even a useful tool in cubes, we all know where this is going once again, don’t we? Terrain Generator is saved from that flat E, though, since it is actually possible that, if you DID put it in a cube, there might be a deck which wants it – not as much, probably, as it would want that fetchland which you should have put into your cube instead, but hey! Still, most of the time it will be a solid last pick, so there is no way that this land crosses over in “D” territory. That makes it an E+.