1: The use of the word Definitely can't be substantiated in an objective manner. Whether or not there is a God is a moot point at best. The rules for adverts say that if there's significant divided opinion about an issue it can't be portrayed as fact.
2: The advert is clearly plagiarising another campaign in order to subvert it, which is probably a copyright violation.
3: The Christian Party who the campaign invites you to join is requesting that you give them a donation and the default option is to give £200.
4: Other bus campaigns run by Christian organisations imply threats to non-christians, saying that we're doomed to hell or some other similar odd possibility. Doesn't this constitute an attempt to encourage dissent between religious (and non-religious) groups?
5: Religious organisations get tax breaks that are just ridiculous when comparable cults like Paul McKenna's weird hypno-toad cult do not receive that by default.
6: Surely, God wouldn't be impressed - didn't Jesus say that worship was something to do privately and that grand displays of piety, particularly with pecuniary elements, were wrong?
Oh dear, I'm going off on a tangent.
It's such a shame that Christianity is being side-tracked by these kinds of stupid squabbles when really the core values of forgiveness, tolerance and kindness are to be applauded and that most Christians believe in the poetry of the bible above its literal truth. I mean, literal biblical truth has David and Jonathan marrying, Jesus having a boyfriend and the most adorable lesbian wedding I think I've ever heard of, but the Anglican communion is threatened with a schism because of who some people fall in love with.
Similarly, Christianity as an ideal is being horribly sullied by evangelical groups making blasphemous claims of their own divinity - just go along the Old Kent Road and see all the "churches" where you have hoardings showing charismatic leaders depicted holding flaming swords, which is clearly semiotic blasphemy. The financial incentives for the leaders of these organisations is another strand which brings faith into horrible disrepute.
Anyway. I'm off to draw more pictures of dinosaurs. Oh, the irony.