If there was anything less suited to me playing on a bleary Monday morning, Portal was surely it. I mean, let’s be honest here – I’m not the sharpest pencil in the box any day of the week, but when it comes to Monday morning I may as well be placed in my chair with a warm mug of Bovril and a simple wooden puzzle to assemble. Giving me one of the most peculiar, interesting and brain-bending titles for years was thus surely a recipe for disaster.

Not everyone will have come across Portal yet, so perhaps I best explain as best I can. Nestled snugly amongst various Half Life 2 instalments and Team Fortress 2 in the Orange Box (from which we will review more in the upcoming days), the game puts you in a familiar first-person perspective but initially sees you without as much as a crowbar for assistance. What gives? How am I supposed to defeat the waves of enemies that will come flooding toward me?

Therein lies the twist: you won’t need to battle any enemies in a traditional sense. Portal is a first-person platform adventure title, tasking you with reaching seemingly unreachable platforms, or using a series of blocks to trip switches and open doors until you reach the level exit lift. This alone sounds rather dull perhaps, but the moment it becomes clear that you have to do so by messing around with portal entrances, exits and the physics created by your use of them things take a turn for the intriguing.

Having woken up in a small test chamber, your character’s introduction to this portal system is gentle at first; in fact, for the opening few minutes the game gives you set entrances and exits to work with. Having a big blue portal opened in the side of your container, you are now able to happily stroll outside and emerge out of the orange exit portal you could previously see on the other side of the window. A bit of tricky shuffling enables you to even see yourself entering or exiting the portal from the other side, giving you somewhat of a headache.

After a bit of jumping about and gentle puzzle solving, you’re handed the Aperture Science Handheld Portal Device. This gives you the rather handy ability to shoot portal entrances – and eventually exits – wherever you please, leading to all sorts of tricks and sports. Gradually as you delve deeper into the game you learn to think more and more outside of the box, placing entrances at the bottom of large jumps so you enter and exit at great speed, or shooting new entrances as you land to put you in a never-ending falling loop to gather speed. It’s tremendously fun to mess around and experiment, even when things go wrong. Hence, the scenario of me having a Monday morning meltdown was averted, much to everyone’s relief.

Portal has two major strengths to aid all this fun. The first thing, and something that doesn’t fully become apparent until you’ve completed the main game through at least once, is that the difficulty curve is judged to absolute perfection. Initial levels err just the right side of easiness to allow you to absorb yourself in without getting too frustrated, whilst as you progress you can certainly feel the game getting harder, but at no point does it seem unfair. You are introduced to the major variables – entrances, exits, switches, turrets and the like – one-by-one, giving you the chance to sample each before having to bend your straining noodle around a room packed full of them. It’s level design and pacing at its finest.

Whilst all this is going on, Valve have you leaping about in the midst of one of the oddest environments a game has thrown up to date. The Aperture Science building is clean and somewhat clinical, yet it’s the menacingly austere robotic female voice that guides you around that really gets under your skin and convinces you that there’s a lot more going on than a mere science experiment. The latter stages of the game see a shift in environment that I wouldn’t wish to spoil for any of you; suffice to say it becomes vastly more unsettling and finishes the main mode brilliantly. After you’ve managed to navigate the main portion of the game there are a couple of advanced map challenges to look forward to as well, with limits on number of portals and the like. Some of them are so tough they are practically hernia-inducing though, so be warned.

There are not many things Portal doesn’t do right, to be honest. In terms of looks it’s perhaps a little behind the times (only a little, mind), whilst the main story sweeps to its conclusion just as you are desperately wanting more to feed into your brain. Other than that, there’s very little to mope about. What there is of Portal is a stunning assault on your brain and ability to think outside usual constraints, mixed in with a dose of Valve humour and resting on the spine of a superb difficulty curve. It’s just as strong as either of two big offerings this winter’s Orange Box brings, and with some luck (and a few downloadable map packs, eh Valve?) it should become the cult classic it so deserves to be.