As someone who used to love Blitzcrank I no longer play him since Thresh patch.
While this has little to do with Thresh himself the mana pool reduction and rocket grab cost increase have been way to harsh. In fact I don't perceive it as an attempt to balance the champion, but as an attempt to throw it in the thrash can (be it successful or not).
-50 base mana
+10 rocket grab cost
*1.5 mana barrier cooldown
with a 240 starting mana and a 120 cost rocket grab Blitz took the shot.
1st level Blitz wasn't exactly strong anyway, so let's jump to 2nd.
Now you have Rocket Grab (120 mana, 20 sec cooldown), Power Fist (25 mana, 9 sec cooldown) and 280 mana.
You execute your trademark combo for 145 mana cost and end with 135 mana.
In 20 seconds Blitzcrank mana regen will give you 28 more mana so you can try again.
135+28-145 = 18 mana.
You're now sitting on -127 mana for your combo.
Blitzcrank's mana regen will take 83,5 seconds to regen that.
Of course we can add itens, runes and masteries.
But 83,5 seconds cooldown I'd expect to do something "ultimate level", but not only can Blitzcrank 1-2 combo fizzle it can also backfire.
I've gone with Taric as suport with a friend of mine and we faced blitzcrank as their support. I gave my friend the following instruction:
"If Blitzcrank pulls me go straight for his carry, I'll use his grab as my gap-closer."
Some levels and he tried to grab my mate, just walked out of the bushes into his grab, soaked the CC and first strike from his carry while my own started attacking theirs.
I hit the ground and quickly Dazzled the enemy carry with a truly, truly outrageous catchphrase and walked in for shatter exhaust.
The enemy carry was quickly dispatched.
I walked away safe and sound.
Don't get me wrong, I do believe the mana barrier nerf was a good and necessary thing. What worries me most is the mana nerfs. It strikes the mana barrier power at early levels way too hard. Not only the cap is weaker but the power goes down faster - so we could say Mana Barrier took a triple nerf.
Keep in mind that the reduction on his mana pool and increase in Rocket Grab mana cost also hurts his gameplay a lot. Blitzcrank has a very limited gameplay with its own counter, no matter how good a player is his kit is very limited on creative strategies options.
Currently Blitzcrank exists to give the tactical advantage of displacing enemies and constanly have some hard-cc available. He does not contribute with sustain, neither does with poke. His damage contribution is inferior to real damage contributing supports and his burst is unnavailable until level 6 (and even then isn't so impressive for burst-down combos as Taric or Leona). This current nerf only open space for him to be outclassed on his true area of expertise in lane (rather than have his weakness exploited to counter him).