Actually, with this song Maiden tried out something new, namely a rhythmic and calm beginning, built around a bass pattern, in which the role for Nicko was nihil or minimal. This was done on various later songs as well, e.g. on The X-Factor, check out Fortunes of War for instance. This song is not only important in this development.
Listen to the part which starts at 2.44, where we hear a certain style, where Steve and Nicko follow eachother smoothly, and Steve does a certain bass pattern and the guitars play the same(!) melody (no harmony, no rhythm guitars). This was done later as well, on various occasions. E.g. take Look For The Truth, take When The Wild Wind Blows:
Afraid To Shoot Strangers is written all over these instrumental sections.