I think there are three things that have accidentally killed modern cinema.
#1. CGI. It is now economical to show on screen anything you can think of... so now anything you can think of can and probably has been put on screen. You know why the shark isn't in Jaws very much? Because the robotic shark sucked. Which forced Speilberg to use it very sparingly... what a twist of fate it would have been for Speilberg to be able to use a CGI shark cheaply. Jaws would have lost its mystery and intensity... it might have killed his career before it started! I just feel that movies today are too... clean. Every shot is a perfectly lit, perfectly framed, crystal clear window into another world. Its perfect. Except its not.
#2. Too many outlets for movies. Multiplex cinemas with 30 screens, DVD, cable, network telivision... there is demand for every concept, every idea and so there are just a LOT more movies than there used to be. So are we running out of good ideas??? I think maybe so! I think in the old days maybe two good ideas were merged into one good idea where as now every little semi good idea is made into a feature that is probably similar to another equally mediocre feature. There is just a feeling of its all been done and we have seen it all before. And the actual good ideas for movies are stretched very thin. Maybe Cameron will wow us with Avatar.
#3. Directors have too much power. I think you need a little balance. In the old days they would pretty much force directors to cut movies down to two hours so studios could get more showings. This was purely a business decision, and granted there are examples where studios forced inferior cuts (Aliens anyone?) But they also forced some much needed discipline yielding tighter, leaner movies. I think directors are too in love with thier own work and are incapable of making objective editing decisions. Movies today have NO DISCIPLINE! They throw in everything but the kitchen sink! Action scenes become boring and repetitive, dramatic scenes lose thier impact, and generally movies are bloated, overdone messes (see King Kong, see the Matrix sequels, see the PotC sequels, see the prequel trilogy, see Spider-man 3, etc., etc., etc.)
To these three things I would add that there hasn't been a REAL movie star in quite some time. Actors today are all pretty boys. Female actresses have actually made some progress I think (although eye candy starlettes will always come a dime a dozen.) But who was the last real leading man??? Being a star is about prescence... and its much, much, much more about voice than looks. That is why Grant, Ford, Bogart, Wells, actually all the legends were legends.
Just my rant. Just my 2 cents.