Bit of a mixed bag this one. Meglos impersonating the Doctor is tons of fun, and I like the idea of a city sent underground because the vegetation has become hostile.

However, it takes a little too long for the Doctor and Romana to finally break out of the time loop, and arrive on the planet Tigella, and bringing back Jaqueline Hill in the new role of Lexa, rather than reprising Barbara Wright is an odd creative choice. Especially as the Doctor is brought into the fold by someone who already knows him from an offscreen adventure. Why not have just made it Barbara who contacts the Doctor, and explained she got abducted from 60s London?