My son has had electronic gaming since a very young age, starting with Lego on the PC and hand-held nintendo games from maybe 4 or 5, then onto nintendo wii, ipod, xbox, ipad etc. He spent a lot of time on Club Penguin and then Minecraft and most of his teens on FIFA.
He's forecast a string of grade 9s in his GCSEs this Summer.
What it has done is given him the endurance to persist, to problem solve, to learn how to plan and save. In club penguin he worked through the various "tasks" and did a fair bit of googling to find pointers as to how to do things. After a while, he was an expert on it and started making his own Youtube videos (at the age of 10). Same with minecraft a year or two later - made some pretty impressive "worlds" and designed his own working "arcade" games using blocks etc. More lately, he's addicted to farming simulator (so am I but that's another story) where you invest in fields, equipment etc to make profits, so it's a kind of business game.
I think it's done him the world of good. Now, when he comes across a problem, say in his school work, he knows how to surf the net for solutions, knows which sources are likely to be reliable, etc - it's massively improved his research abilities.
It all depends on what they're doing on their computers/consoles. If they're playing mindless games, then maybe not too good, but if they're playing games requiring logic, games which enable you to create worlds etc. decision-making, exploring options, etc., then it's a good thing.