Nikolay Baryshnikov (VP of Interactive Entertainment at 1C) did a great interview with last year (you’ll need to register to read the article). My favourite quote from which was this:

I might sound stupid but my honest belief is that, in the games industry, nobody has a clue, why that product is successful and that product is a failure. You can do everything right, you can have a proven IP, you can have a great marketing budget, a great game – but nobody buys it. Or you can have a game which the press say is worst game ever, has 10 per cent rating and sells like hundreds of thousands of units, day one.

It was great to read this because it’s an opinion I share also. Sure, you can analyse hits after the fact and determine why they became successful – but there’s no skill involved in that. So really the skill would be to predict which games are going to be successful – but like Nikolay says – nobody has a clue. So what’s left? All you can really do is trust your instincts and make the best game you possibly can.