Google finally released a calendar app for iPhone today. Even Google's own blog post title says "[...] It's about time". I couldn't agree more.
My early tests show it is based on the (released in November) updated Android app which simplified calendar management (transforming GMAIL events into calendar entries automatically). Like Fantastical, it also has an Assist feature which helps you fill our the various pieces of a calendar entry.
Here is the direct link to the app on iTunes (link) , I couldn't find it with the itunes Search feature.