I was pretty happy with Indy 4 - about the only thing that bothered me with it was the last 10 minutes. Everything else, considering the age of the actors, was great I thought. They captured the 80s movie magic a lot better than I had expected.
For Indy 5, I really don't want to see any sort of alien stuff either. I doubt we will... that would be two films in a row with a similar theme... doubt it's gonna happen, but I would love for Indy to find out about some former Nazis in Brazil who are gathering some sort of religious artifacts, and the adventure leads back to the Middle East with Sallah... I'd be fine with Indy, Mutt and Oxley teaming up with Sallah for a finale to the series.