Marco's place is perfectly positioned for seeing historic Rome (so glad we chose to stay here rather than Trastevere as advised by a friend). You really can easily walk to the main sites: the Pantheon is very close; while Vatican City, the Coliseum, the Trevi Fountain and the Spanish Steps are also very walkable. Ditto the Villa Borghese park (for the Borghese Galleria, the Galleria Nazionale d'Arte Moderna and, if you've had enough high art, for some fun on 4 wheeled pedal bike/carts).
The apartment is also perfectly located for eating out, being on a street that is home to some great restaurants (Baffetto's pizzas are excellent), bars and gelateria, as well as a mini Carrefour that seems to stock pretty much everything despite its size.
Marco himself is a great host - very helpful, friendly and fun. We also appreciated his generosity in supplying us with breakfast vouchers for a very nice local cafe for good coffee, pastries and, depending who was serving you, some delicious freshly squeezed orange juice!