Werner Heisenberg in 1927
Theoretical Physics has been a victim of its own success. The Discovery of the Quantum Field Theoretical equations that lead to Asymptotic Freedom (how quarks and gluons interact) in 1973 by Politzer, Wilczek, and Gross was the last truly BIG advancement in (Theoretical) Physics. That quickly led to The Standard Model of Particle Physics, which may very we be the greatest achievement of Humanity, so far, to date.
There has been improvement in terms of tightening up the equations a bit, and Experimental advancements, such as the confirmation of the Top Quark. Almost every thing else has been speculative, including String Theory, AdS/CFT Correspondence, Loop Quantum Gravity, Causal Dynamical Triangulations, and speculative theories of Dark Matter and Dark Energy.
What's on the table for the next few years is the LHC, which will confirm or deny the existence of the speculated Higgs boson and Supersymmetic particles, and the great Astronomical observatories which will tighten or change our views of the 2 Relativity theories, so the age of the Experimentalist will likely crowd out the Speculators in the coming decade.
Which is why Theoretical Physics disappoints me at the moment, it's in a "stall" mode, so I've decided to let it go for the time being in favor of Mathematics. :-)
There's plenty of work to be done in Mathematics, and the demand outweighs the supply.
Unlike in Theoretical Physics.