I do hope this will be the last one. It is time either to let the torch finally burn out or let in a young flame. Not sure if a young Indiana Jones would work as it would not be the Jones as we know and like (at least the first three movies) but time will tell. I would not mind something completely different either, I feel it has been sooo long now since we have had a really good adventure movie. I still watch The Mummy with Brandon Frasier (Pirates of the Caribbean series is also very good) from time to time just to get that good feeling of adventure again. I tried watching the Mummy reboot with Tom Cruise, but Hollywood can't make it work because they can't write a bloody good script!
Hopefully it is the last one, and I don't think that continuing the series with a younger actor as Jones would be as successful either, it would be better, in my opinion, just to start with a new series as well as actors. Even it was in a similar vein of subject matter.
I enjoyed the Brondon Fraiser Mummy movie as well as the Pirates of the Caribbean movies, but couldn't get into the Tom Cruise Mummy film. I tried watching it about 3 times I think, and either fell asleep or turned it off somewhere around the 3/4s mark as it just couldn't hold my interest. It had some really good special effects, but that was about all, well, and the fact that Sofia Boutella was the sexiest mummy I had ever seen in any of the Mummy movies.