There are alot of reasons why Russian and US subs look different. Most Russian subs are more robust in the sail area for 2 reasons ,one is that they are made to punch through much thicker ice caps than can american subs and two the base of Russian subs are much more rounded to reduce drag and with no sharp angles are less reflective to enemy ASW vessels. American sub sails ( conning towers) are "slab "like in shape and have very sharp ( 90 degree ) angles were the sail meets the deck.
The hulls are shaped differently also because the Russians favor a double hull design. This affords much greater protection against ASW weapons. In the double hull design the outer hull has many very large ballast tanks and bouyancy tanks. Also in this hull can be stored the weapons such as cruise missiles,mines etc. The inner hull is now much more protected from the blast of a torpedo as it now must blast open the heavier outer hull and various tanks which in turn act like a blast barrier. the larger double hull can also store various sonar equipment,air bottles and other things that would otherwise have to be stored inside the hull if it was only a single hull boat. There are other reasons but this is a good beginning.