  The recent observation of correlated phases in transition metal
dichalcogenide moir\'e systems at integer and fractional filling promises new
insight into metal-insulator transitions and the unusual states of matter that
can emerge near such transitions. Here, we combine real- and momentum-space
mapping techniques to study moir\'e superlattice effects in 57.4$^{\circ}$
twisted WSe$_2$ (tWSe$_2$). Our data reveal a split-off flat band that derives
from the monolayer $\Gamma$ states. Using advanced data analysis, we directly
quantify the moir\'e potential from our data. We further demonstrate that the
global valence band maximum in tWSe$_2$ is close in energy to this flat band
but derives from the monolayer K-states which show weaker superlattice effects.
These results constrain theoretical models and open the perspective that
$\Gamma$-valley flat bands might be involved in the correlated physics of
twisted WSe$_2$.
