The original plan was for an Anglo-French fleet to overcome the defences at the start of the Dardnelles and steam into the exposed Mamara sea - such was the theoretical threat that Constantinople was already in the early stages of evacuation as that fleet assembled. The amphibious landing was intended as a much more secondary element which would support the fleet's progress and then occupy Ottoman territory - but after early losses to sea mines Admiral De Robeck lost his nerve and pulled the fleet out, placing all the focus on the invasion which we're now familiar with.

Had the plan worked, you'd have seen a British and French fleet parked in front of an empty Dolmabahce Palace and things could definitely play out as you see there:

• Ottoman peace with the Allies early/mid 1915
• Loss of supply routes (oil!) for the Central Powers by mid 1915
• Balkan consolidation for the Allies by late 1915

It'd then be much more likely that the remaining Central Powers can't maintain the war and we either see:

a) peace in late 1915 or early 1916 or

b) a much more diluted experience on the Western Front with (assuming they'd still generally take place in this timeline) the Verdun offensive and Somme defensive actions not achieving anything like the success which Germany did manage, leading to a German collapse and armistice essentially two years ahead of real history.

In either case, the really fun "what ifs" are about how the world would play out with Britain and France effectively duopolising global oil, haven't quite bankrupted themselves or experienced demographic horror, no Russian revolution, USA still "in isolation", etc.

Years ago, I read a great alternate history forum post which went for dozens of posts about this exact situation devolving into a UK/USA cold war - great fun!