A huge moral booster for the Entente and the opposite for Germany-Hungary.
UK would not have to spend men, money, time and effort in Egypt or Mesopotamia. If the Ottoman surrender was due to Gallipoli the siege and surrender of Kut would been avoided.
Russia wouldn't have to fight in Kaukasus and, since Bulgaria probably will stay neutral, less in Balkans. That, combined with Cymraegs point of export/import, will almost certainly mean no bolsjevik revolution. Germany and Hungary will be forced to fight on the eastern front.
Italy would probably still join the Entente - a lot of bribes and influence had already been spent, and the enemy had just become far weaker.
But the Allied advantage can't be used in anything else than bloody attacks against trench systems. I doubt that "the cult of attack" would allow anything than even bigger Somme (but maybe more prepared, since there would be no need to help the Russians). Would it be possible/meaningful to attack through the Balkans against Hungary?
Germany may be tempted to launch unresticted submarine warfare earlier, which would mean an earlier US entry into the war. The German military leadership were sometimes very stupid in this way.
My guess is a WW1 that ended slightly faster (1917?) and with fewer dead. The Paris peace negotiations would be completely different with Russia still in play. Would they go for the ultimate goal, Constantinople? If Gallipoli was a success Churchill would still be in power and maybe become the PM during the 1920s? Would the Ottoman Empire survive? The Middle East would anyway be totally different.