ACCESSIBILITY:
Easy to reach by air. By boat it is possible but takes too long and to me it makes sense only if you are a European taking your own car rather than spending a bunch on a rental car.
TRANSPORT/GETTING AROUND:
A rental car almost a must. Public transportation exists but not frequent and therefore would severely limit ability to see the islands efficiently.
COST/ACCOMMODATIONS
Expensive and few vacancies from mid July to end of August. Much more affordable outside those periods. Sardinia (Italy) substantially cheaper than Corsica (France).
CULTURE
They have it.
THINGS TO SEE
Historical: some, but not as much as other regions in the continent
Natural: a whole lot, on mountains, hills, beaches and cliffs, under water.
Beaches: probably the absolute best in the Mediterranean (applies to both Sardinia and Corsica)