Of all the problems I had with Indy4, the aliens weren't one of them. Yes, the movie definitely took the series to new territory with the alien 1950s B-movie stuff, but Spielberg still kept it to some extent grounded in a 1930s serial style as well. There were people jumping from moving cars onto another, there was vine swinging, there was running away from killer natives... the Republic serial stuff is still a big part of Indy4. And the Marshall college chase was wonderful, traditional, classic Indy.
If anything, the strife between Lucas and Spielberg is a healthy thing for the series, because it ends in compromise that's (theoretically) good for the audience. Lucas got his wish to bring the series to a new place, while Spielberg balanced things out by putting enough "vintage" stuff to keep it distinctly Indiana Jones even if thematically it stands out from the others. I would imagine that would continue with any Indy5, and I'm all for that.
The problems with Indy4 (and there were many) were entirely screenplay related, not story related. It feels like they spent so many years trying to agree on a story, that they just signed off on the first script that met all their personal needs in terms of plot (Lucas got his aliens, and Spielberg/Ford got crystal skull/conquistador stuff to tie it enough into archeology that they could get over flying saucers). Once Koepp's script pleased everyone from a story perspective, they should have refined it until the storytelling was top notch. It wouldn't surprise me at all if the Writers Strike kept Indy4 from having a script that was as good as it should have been. Wasn't Koepp redrafting screenplays during shooting? When they kept reiterating for the past 19 years that they were "waiting for the perfect script," what they really meant was that they were waiting for a script that had enough alien stuff to please George but enough traditional stuff to please everyone else. That has nothing to do with structure, dialog, characterizations, and all the other things that Kingdom of the Crystal Skull fell really short on and ultimately made it the disappointment that most people consider it to be (to varying extents).
My two requests for Indy5 would be: a better screenplay, and telling Kaminski to back the hell off on his overbearing lighting style. If you're going to run the movie through a DI and make it look all digital, hazy and artificial, what's the point of shooting it on film in the first place? "Approximate Slocombe's style" my ass. In terms of the shot compositions, the cinematography was decently reminiscent of the original trilogy and stands out as old fashioned among modern blockbusters (in a good way), but the color and overall look of the film was agonizing.