My biggest impression: It was a lot of fun. I grinned and giggled a lot.
Aside from that, there was a lot of very unneccessary and fake-looking CGI throughout the film that really took me out of the movie at times.
I would consider it an "epilogue" chapter in the Indy series. Sort of an optional bookend to the real meat of the trilogy stories, i.e. "what did Indy do when he got old?"
If Lucas wants to make more after this, that's fine with me. They aren't necessary, but I'll still enjoy watching them. I just won't put them in the same category as the originals.
--SKot