Team Fortress 2

As well as kit that changes how a class is played, there's plenty to tweak the default load-outs: you can give your Engineer a faster-building mini sentry gun if you forgo the ability to upgrade it. As a Medic, you can choose a Medi-Gun that makes you and your target invulnerable during ubercharge, or one that gives your target invulnerability and critical hits.

Such a kaleidoscope of weapons, abilities and buffs is overwhelming, and there will always be the hipsters insisting that vanilla Team Fortress 2 is superior to its current form. If you agree, there are servers for that. But next to this much fun, such po-faced solemnity seems lunatic. Is it balanced? Who can say. Nothing feels unfair - and considering the bullets, baseballs, darts, arrows, rockets, bottles of piss and numerous other tools you'll face, that's saying an awful lot.

But no matter the class or load-out, Team Fortress 2's standout quality is the way it makes you use it. It's the one team-based game that feels team-based in every single match, because everyone has to play to their strengths. Even in the best of TF2's competitors, such as Battlefield, a medic can still have a submachine gun in his back pocket and get a killstreak. TF2's medics are too busy healing.

A lot of stuff we assume is ubiquitous in shooters - grenades, assault rifles, recharging health, straight-up deathmatch - just isn't here. Team Fortress 2 doesn't use the genre's crutches. It absorbs and transforms the best of its inspirations: the original Team Fortress was a Quake mod, and what are the Scout and the Soldier but aspects of Quake turned into entire classes?

Beyond its fundamentals, Team Fortress 2 is an aesthetic achievement that looks more towering with each passing year: it still looks better, and is clearer in-game, than every other shooter. At the time, Tom said: "Other FPS developers: copy this immediately." No-one has.

It combines this with irresistible characterisations that are funny in isolation - the 'Meet the Team' videos, the in-game manual belonging to the Engineer - but funnier in the thick of things, when the classes let rip with their brilliant, endless one liners. There are so many details to admire, practical and otherwise. The composition of your team being on-screen while choosing a respawn class. The zoomed-in snap of your killer. Taunts that can kill.

Best of all is the 'ding' sound effect. It can be turned on in the options: every time you hit an enemy, ding! It changes your game utterly. I never used to blanket-bomb chokepoints with the Demoman, but with dings turned on I realised it created symphonies. The Heavy's optimum range is clear as bells. And for the Pyro, it's a manic alarm bell while someone roasts.

The free-to-play model doesn't change much for Team Fortress 2. Being an existing owner, I set up a new Steam account to try out the service from the perspective of a scabby freeloader. It's hard not to do a double-take when everything works - TF2 for free! It's not even fair to call it a bargain. This is an incredible gift.