The easiest way to describe Research and Development is “Portal without portals”. Aesthetically, the two games have nothing in common: the former is set in a world of rusted iron and toxic sludge, the latter a pristine laboratory. What they do share, however, is the same basic structure. Both are essentially a series of discrete puzzles embedded in an overarching narrative.

Said narrative is a lot sparser in R&D’s case, but it’s presented in the traditional Valve manner: dynamically, via the environment. Once the game begins, developer mbortolino never makes the mistake of bogging down the fun with expository cut-scenes and what-have-you. If you want the story, you have to look for it yourself.

Whether it’s worth looking for is another question entirely. I’m inclined to say not. It isn’t a bad story per se; it’s just kind of dull and unnecessary. Think of it as the forgettable topping on an otherwise delicious cake. A delicious cake made of puzzles.

Each new area you visit in R&D presents a new challenge, with objectives ranging from the mundane (plug in a generator) to the heroic (destroy a helicopter with its own bombs) to the bizarre (align a series of coloured crystals and shoot a laser through them). Consistent through all these is your lack of weaponry – the only gun you get is the good ol’ gravity gun, and even that doesn’t become available till about a quarter way through. In those rare instances in which you’re required to defend yourself from aggressors, you’ll have to do it creatively, using the environment to your advantage.

By and large, mbortolino’s puzzle design is meticulous and unforgiving: where Portal was an expertly scaffolded learning experience, R&D is a demanding slog punctuated by constant death. But in a good way! Because the game gives you little in the way of help, the sense of accomplishment you get when you overcome its challenges is considerable. In a word, R&D makes you feel proud for beating it.

The obvious downside to this is that R&D is also sometimes excruciatingly frustrating. Many of the puzzles are the equivalent of complicated time bombs: either you figure out what to do quickly, or you get killed. On the one hand, this serves to imbue otherwise staid situations with a sense of desperate urgency, which is not entirely unwelcome. But on the other, bigger hand, it also means you end up doing the same puzzles over and over again. This becomes especially infuriating when you know what to do, but lack the reflexes or manual dexterity to do it. Portal suffered from the same problem to a certain extent, though in R&D’s case it is – unfortunately – much more pronounced.

However, that shouldn’t stop you from giving R&D a whirl. Difficulty spikes notwithstanding, it’s still pretty much the perfect single-player mod. It’s unique, clever, and (for the most part) remarkably well designed. Moreover, since the majority of its assets – including models, textures, and sounds – are taken directly from Episode Two, it is also a relatively miniscule download. All things considered, there’s really no reason NOT to try it.

So, think you've got the IQ to make it through R&D's challenging puzzles without having an aneurysm? Here's what you'll need to play the mod:

1. You'll need to have Half Life 2, Episode 2 installed, with the latest patch.
2. Click here to download and install the full Research and Development client.
3. Sit back, relax and prepare to be humbled.