If you could only play one game for the rest of your life, what game would you choose?

I came across this question recently on Kotaku. Since then, I have spent much more time thinking about it than I ever would have thought necessary. It's a tough question!

Your first instinct might be to choose your favourite game at any given moment. Right now, I'm really enjoying DJ Hero over all other games, but I wouldn't want to play it for the rest of my life. I know it'll grow old before too long. Or you might think about the best game you've ever played. Portal is one of the best games I've ever played, but after playing it through twice, most of the reply value has worn off. I wouldn't want that game either.

I might have been quicker to choose a game when I was younger. At various times, I might have picked Bubble Bobble, River City Ransom, Street Fighter II, SimCity, Dr. Mario, Doom, WarCraft II, or Virtua Fighter 4: Evolution. But none of these games strike me as being the One Game anymore.

It would need to be a game with lasting power. It would need high replayability. I would like a game with action—sims, puzzlers, and classic RPGs are fun, but, with only one game, I would want to be in direct control of someone doing something. But I would also like the ability to choose from a selection of characters and be able to customize those characters for different play experiences each time—many FPSs would get eliminated here, as would games with only one character with a linear power-up path. I would want a large world to explore—that leaves fighting games out. And, thinking on perspective, I would prefer third-person to first-person: given the choice, I prefer seeing my character.

Ultimately, considering all these criteria, the game I would pick, I think, is Diablo II. It's not my favourite game of all time, but it's a good game, and it's highly replayable. Seven characters. Lots of customization through skills and equipment. Randomly-generated worlds. Multiple difficulty levels. Sure, mouse-clicking isn't the most intense action, but it's better than a classic RPG. Plus, you could spend AGES collecting the unique sets of randomly-dropping equipment.

I considered a couple of other action-RPGs too. I considered Titan Quest, but its maps aren't randomly-generated, and you can only pick between a generic male and female character. I also considered Torchlight, but it has only three character classes, and I haven't yet played it enough to see how deep it runs. I might have picked Diablo III, but I don't want to commit myself—even hypothetically--to a game that isn't out yet.

So, yeah, if I could play only one game for the rest of my life, I would choose Diablo II.

What about you?