I play Blitzcrank with some regularity and I think he is actually really fun to play as. I read a lot of things on here that sound like his initiation ability is all in the rocket grab. I want to put in my 2 coppers that this isn't completely true. You are definitely not a beefy tank. You are fairly squishy, but you have a lot of power in fear.
People do not want you grabbing them. People do not want to be knocked up. I go with an AP build including sheen and when push comes to shove I get a kick out of rushing them with a nice knock up and burst. You get a pretty nice damage output from this. Usually people freak because they fear the pull. I find it perfectly normal to smack the one that runs slowest and ruin his day a little because the others are running, then you can keep him from running with grab.
If they end up focusing on you, you will die more than likely. Probably 70% of the time. The upside is that it will usually take them just enough time for you to fire off every ability you have - dealing out damage and buying a little time for your team to beat on them. You won't be a kill machine, but you should get a LOT of assists by being that team player everyone relies on to pull/rush in like a heroic fool and make their lives less predictable and a lot more annoying. A hit and run burst that gets them wasting spells on you/chasing you while you sprint home can be a really effective way of letting your team wail on them a while.
Hopefully that is somewhat readable and intelligible and that it actually helps!
tl;dr: Blitz is fun to play and he can do more than rocket grab for his team.