Yep, he does completely change the game, but this also has its own weaknesses. Furthermore, Blitz is pretty strong, but not unbeatable - there is a reason he is RARELY picked in high elo - it's because at high levels of play, his hook predictable and easy to dodge, and if you don't land hooks as blitzcrank, you essentially fail to do your job. Let me give you some anti-blitz tips:
1.) He has no way to protect his own ADC - if you can poke his ADC out from behind minions, and keep him from engaging on you, his hook becomes meaningless.
2.) His hook has a very long cooldown. After he uses it and whiffs, there is a LARGE window where he is basically useless. Take advantage of the window. Don't be scared if his hook is down.
3.) Morgana is an EXCELLENT counter to Blitzcrank. Pick. Morgana. Her shield essentially negates his hook.
Failing that, Janna / Taric / Karma are all excellent picks to deal with a good blitzcrank.
4.) If your hooked, your teammate should immediately engage on the enemy ADC. Let me give you an example, let's say I pick 'support' Annie against a blitzcrank, Youd think this would be a shit matchup.. but I'll just sit on my stun while the blitz sits on his hook. If my ADC ever gets pulled, I will nuke the everliving bajeezus out of the enemy ADC, to ensure they don't win that trade. So in essence - CC the damage potential and the hook becomes meaningless. A well-timed exhaust can save the day here.
5.) Finally, and perhaps most importantly - you need to understand map pressure. A Blitzcrank almost always wins his lane by the threat of his hook, This means he will often be up on your tower, trying to push it. This is a very vulnerable position - Just Ping and ask your jungler to come gank. Blitzcrank is SO vulnerable to good, smart ganks. If he's spending his time under your turret, get yo' Jungler.
