Applied Materials interview questions

I had 3 rounds of interviews with different levels of managers who went through the complexities of the projects I had worked on in the past. One interview also involved designing a distributed system and how different traffic loads would be managed. The interviews were wrapped up in a week and I received a verbal offer next week. I waited for the offer letter for 4 weeks and the recruiter still do not have released an offer letter for me, citing that the finance department has not approved my offer yet. The process was very frustrating and totally unexpected.