We study the landscape complexity of the Hamiltonian \(X_N(x) +\frac{\mu }{2} \Vert x\Vert ^2,\) where \(\mu >0\) and \(X_{N}\) is an isotropic Gaussian random field on \(\mathbb {R}^{N}\) . We derive asymptotic formulas for the expected number of critical points of the Hamiltonian, as the dimension N tends to infinity. These results complement the corresponding findings for locally isotropic Gaussian random fields, as well as the work of Auffinger and Zeng (Auffinger and Zeng 402:951–993 2023, 2022) on non-isotropic Gaussian random fields with isotropic increments.