Valve is one of those developers that never seems to put a foot wrong. Whether it's Portal, Half-Life, Counter-Strike or Steam, everything it does seems to come up smelling of roses.

But it hasn't always been that way. The much-loved studio has made some big errors in its time. How do we know? Because its key execs have admitted it.

In fact, they've revealed their biggest howlers of all time. And it makes for eyebrow-raising reading.

When PC Gamer asked Valve's Gabe Newell, Erik Johnson and Doug Lombardi what the company's biggest failures had been, they received a 'deluge', including:

"Moss in the original Half-Life" - where Valve had intended the game's simulation to be so lifelike that bryophytes would grow in real-time.

"Ricochet" - Valve's TRON-style multiplayer disc-throwing game.

"PowerPlay" - a networking game Gabe et al worked on for a year before abandoning.

"The first few months of Steam."

"It's hard to say now, but the first two days of Half-Life 2 - that was a failure."

"Prospero, the game we never shipped. I mean, we still think about it, right?"

"The Team Fortress 2 that was built up until 2000."

"The second TF2."

"The Riot Shield," added Newell. "But that was small on a failure scale. That was an interesting failure, because that made us think hard. It's the first time we put a feature in and more people played the game, which is our most basic way of measuring whether or not we're making people happy. And then we took it out, and more people played. And we were like: Okay, what does this mean?"

Lombardi added that: "Counter-Strike continues to mystify. Well, no in general it taught us a lot about the value of constantly touching your customers."

"Right," responded Johnson, "so our customers are responding to this more like a... service than a product!"

They say true genius is its own harshest critic. That's all we're adding.

You can read the full, fascinating interview with Valve on its history in the latest issue of PC Gamer UK - which is with subscribers now and in stores tomorrow.

Either Half Life 1 Source (a big missed opportunity) or Left for Dead 2...

The big failure for me was (I think HL2) needing an internet connection to install/play a single player game mode. Seems a long long time ago now though.

Er... is that allowed?

It depends. What's the average age of a gamer?

The Cheeky Girls think so. And when have they ever been wrong?

A new career for the cheeky girls? Marketing consultants.

They've got as much experience as the professionals anyway... and a former political contact

Most marketing people are so full of sh1t anyway. They could not be any worse.