What is by far the most likely diagnosis?
Glioblastoma (WHO grade 4 astrocytoma).
What other entities should you consider, although all a far less likely?
Large necrotic metastasis, subacute infarct, tumefactive demyelination, radiation necrosis.
What other sequences would be useful in the work up of a suspected glioma?
MR spectroscopy (to increase your certainty that this is a glioma) and perfusion (to identify regions with highest Cerebral Blood Volume, to help target highest grade). In this case all the tumour will be grade 4 most likely.
MRI of the brain demonstrates a large heterogeneously enhancing tumour in the left parietal lobe extending down towards the ventricle. It has a non-enhancing central fluid signal component suggesting central necrosis. There is surrounding oedema with mass effect.