Terry Chilvers, that I was sure I'd left behind in another life. The first was the old console vs PC argument, in which we quickly established that if good, fun, AAA is your thing, stick with your black box; if experimental, meaningful, cutting edge experiences are what you're about, then you can't afford to miss the likes of The Void and The Curfew.
The second was achievements. I recalled sitting next to some Sony guys at a Develop conference a few years ago and being a little taken aback by their admission to largely playing games for GamerScore nowadays, and it reminds me that our industry is still very much polarised by those who see it as a new form of expression, and those who see it as a time sink.
Pro No. 1 - More Players
The first benefit of the meteoric rise of achievements is - to my mind - the simple encouragement it provides for players to play more games. As noted by a satire like Armor Games' Achivement Unlocked (my thoughts on that here), achievements are an incredibly sharp and effective application of player psychology. I am, most likely, no more thrilled about a legion more thirteen year old CoD players joining the ranks than you are, but ultimately more players - no matter what they're playing - is a good thing for our industry moving forward.
Pro No. 2 - More Ways to Play
The other, oft-neglected purpose to which we can set achievements is in guiding players into enjoying a game in new and inventive / emergent ways. Online games in particular tend to see the development of player-pioneered gameplays - eg the rocket jump - and a cleverly designed set of achievements such as those in L4D2 can open up ways of playing that a tutorial simply couldn't cover. My favourite implementation of this was a game Jim mentioned - whose name I've forgotten, Jim if you're reading help me out here? - in which every achievement was themed around failure: blow yourself up with a grenade; kill the president's daughter...
And the Inevitable Con
While there's plenty of good that can be done with achievements, for me they fail to outweigh to big drawback - that achievements are encouraging players to regress in their expectations of interactive entertainment.
Achievements insist implicitly that players 100% a game. They insist that players see a game as quite literally a 'game' - a challenge to be overcome. They break immersion. Finally, they draw out addictive behaviour.
I love a good, AAA romp. Sometimes I want to switch off my brain and blow some shit up. Same applies to film, music and literature. What I desire most of the time, though, is for interactive entertainment to be smarter, more mature, and more valuable a way to spend time. The principle of someone sitting on the sofa with a huge bag of Doritos playing GTA IV for 36 hours straight just for the GamerScore is one I find reprehensible - it puts our industry firmly back in the 'games are for geeks' stereotype of yesterday. That some players genuinely buy awful games just for the low hanging fruit makes me sick to my core. To be clear, I don't believe everyone is like that, but I feel there can be no doubt that the sort of beautiful, singleplayer experience provided by something like Braid is largely antithetical to the concept of achievements and the mindset they breed.
My position is largely summed up by Terry's observation in the pub: achievements are exactly what a non-gamer would expect games to be about.