Movies are great for many reasons, but having a superstar actor/actress can make even a half-ass movie bearable or even good. There's lots of great actors who can pull it off these days. To give a few random examples. Benicio Del Toro. Bruce Willis. Brad Pitt. Clooney. Clint Eastwood, after all these years. ... much as I hate to admit it, Leonardo DiCaprio.
We used to have them. Just looking at the 80s & 90s: Sigourney Weaver pulled off many hits, including Alien, Terminator, ... RenÌ©e Zelwegger was awesome headlining in Bridget Jones, Nurse Betty... Jodie Foster carried Silence of the Lambs & Contact. Meryl Streep, Katharine Hepburn, Kim Basinger.
Where are they now? They seem to have faded away. Julia Roberts seems to be gone. Zelwegger is doing voiceovers. Foster hasn't been seen lately. Hepburn is out of town, and Basinger seems to be mainly in movies I haven't heard of.
Does Kate Winslet count? Uma Thurman? My theory is that there's still great actresses out there, but they're not getting good parts.