When everything's set up right, Orcs Must Die! feels very good indeed. The crowd will burst out of the doors and the first few are instantly spiked; the next lot, tumbling over their corpses, get stuck in tar as arrows shunk through them; then a steam trap levitates the survivors into the sights of a row of archers to create a load of pin cushions. A straggler somehow avoids all of this and sprints for the rift - and just before reaching it, the last-ditch Paladin you hid behind a corner slices his head off.
Even when you get it wrong, the game gives you the tools to recover. Any trap can be sold for its cost to change layouts on the fly. Sometimes, what seems like a perfectly-positioned set of death-dealing blades get bypassed, or a hunter enemy gets among your archers and guts them, leaving you with a load of sprung devices and a popgun. At these moments, Orcs Must Die! can be amazing, the interface coming into its own as you fight a desperate rear-guard action, shoving spike traps and arrow walls into every remaining crevice, tossing down exploding barrel after exploding barrel and just making it by the skin of your teeth.
Great stuff. And then, about halfway through the second of three acts, Orcs Must Die! becomes a very tough nut indeed. Your initial spending money seems measly next to what you have to face from the off, there are multiple spawn points and no way of telling which one will open first other than a trial and restart, and one wildcard enemy throws all your plans in the dustbin. Part of this is an enjoyable challenge - being able to adapt quickly and maximise what you do have. And then at other points a huge mob of miniature sprinters will materialise, run past all your traps without being hit and straight into the rift and that's that.
Next time you'll be prepared, of course: but was there any way of telling that tactic was coming other than losing to it? The start of each level does show the icons of the enemies you'll be facing, but the sheer mass of enemies in later levels means your strategy always has to be general ('kill lots of things as efficiently as possible') rather than tailored towards stopping one specific type. There are a lot of spikes like this, certain points in certain waves, that simply flattened me: the first half of the game is easy street, the second scales up to something rough indeed.
Difficulty is a subjective thing, so the rapidly-scaling challenge in Orcs Must Die! may work for some players. You could argue that managing these crisis situations is exactly where the meat of the game lies. I found it extremely frustrating after a certain point, with progress depending on a lot of trial and error.
There are other disappointing aspects: certain traps, for example Push Walls and Barricades, seem so limited in function they barely get a look in - while others are constants. There's an upgrade available for each of the 28 tools and traps, but while some of these make them more efficient, a lot simply make them cheaper to buy, which feels like a failure of imagination. Upgrades are purchased with the skulls you get for clearing each level, awarded on a five-skull rating system which seems all over the place: I cleared one level without taking a hit and without a single enemy getting into the rift, and got three stars. In another I barely survived with two Rift points left and got five stars.
Bewildering stuff, really, but Orcs Must Die! does more right than wrong: its best trick is your integration as the 'hero' character amidst all the usual contraptions, combining that tower defence skill of balancing fixed positions with the ability to get in the mixer and manipulate the crowd. Rewarding and frustrating in equal measure, but rarely boring, it's a memorable dose of mass slaughter.