Of course it is. If you just wait a few months, very often you get all the DLC, all the patches for the best experience and you pay a fraction of the launch price. It depends on the game, though. Nintendo games never get significantly cheaper and they come without major bugs, so you're good to go. But with games like Battlefield, it's just silly to buy at launch. Such games lose value so damn quickly, it's not even funny!
For me personally, there are just a few exceptions from this golden rule. I always buy Fallout at launch. I know it seems silly, because everything applies here just like with other games. But I friggin' love Fallout to death! I also never ever play the DLC from Fallout. I don't know why. I didn't do it in the past and now it has become kind of a ritual, lulz.
I also buy GTA right at launch, because that sucker takes his sweet time to get cheaper.
Then there's Civilization. That one gets cheap rather quickly, but screw it. I'll be playing each new iteration at least a thousand hours until the next one arrives, so spending 50 € isn't asking too much.