I no longer play World of Warcraft and haven't for over a year. However, I do not regret in the least the four years I spent on it, and dollar amount that I am unwilling (too lazy) to calculate.
What do I REGRET buying? Well, this may sound like BS, but I really don't regret any of the games I've bought. I am struggling to come up with even one example of a game I bought and then disliked.
Actually, wait. The Witcher. I bought a used copy, so I barely spent any money on it ($10, I think? Maybe it was $20) and I enjoyed the first chapter a LOT. I was really enthusiastic about the game, and it took a turn for the worst in the second chapter. I don't even remember how many chapters the game had, but I wasn't even at the halfway point yet (it is a relatively long game, compared to recent stuff). I just couldn't stand the complete change in gameplay, and it was no longer fun.
Even then, it wasn't a total waste. I definitely enjoyed it for a while. Probably for longer than most single-player games even last these days.