The war in Syria reminds me a lot of the Spanish Civil War, with its huge role of foreign adventurers, the clash of international ideologies, the largely static nature, the role of local militias and finally the intervention of foreign powers with air power and limited ground forces.
The Western powers would like to see Iraq back to status quo ante, the Assad regime removed and the salafist extremists (particularly daesh) eliminated.
This set of extremist war goals is almost certainly too ambitious in context of an extremely weak hand. The Western-aligned FSA forces are the weakest or 2nd weakest faction on the ground, despite what Western support arrived so far. Western war goals are thus not pushing to a quick end of the Syrian ordeal.
Russian and the old regime prefer a return in Syria to status quo ante, with Assad emphasizing his own power and Putin emphasizing Syria's role as a Russian base if not proxy in the region. This set of war goals is quite ambitious as well, but I perceived a willingness to accept some power-sharing deal with other factions (Kurds, FSA), so it's not as extremist as the Western one.
The Shi'ites - partially overlapping with both previously mentioned factions - want to protect the Shi'ite minority in Syria from Sunni domination and want to maintain the Shi'ite domination of Sunnis in Iraq. The latter appears to be feasibly militarily under the condition of continued Western air support, and the Shi'ite minority regions in Syria appear to be quite safe in light of the Sunni-dominated factions' inability to advance any more. I suppose the Shi'ite goals don't quite let Iraq calm down for good, but at least in Syria they are likely destined to achieve their goal (at least for the regions with large Shi'ite populations or even local majorities).
The Kurds still want to establish autonomy first, with Kurdish independence later. They have largely achieved the necessary successes in warfare and are likely going to achieve some more, but the 2nd, long term, goal is blocked by Turkey. They cannot deal with Turkey with violence, and the current Turkish government appears to be both utterly uncooperative with Kurds and fortifying its power with a move towards autocratic governance. The preliminary goal of autonomy isn't a real obstacle to peace, though.
Daesh's war goals are bonkers and they showed almost as much talent in acquiring additional enemies during wartime than the nazis, so let's ignore these losers' policies and outlook.
Finally, there's Turkey, which is the most influential foreign power in Syria due to its geography but doesn't use this much yet. It was apparently an enabler doe daesh's rise, is now (after having good relations before the Arab Spring) an opponent of the Assad regime, a NATO member (thus supposed to be pro-Western by default) and in an almost hysterical opposition to Kurds (because recognising them as a nation would attack the foundations of the idea of a Turkish nation and cost the state of Turkey much territory).
I suppose daesh will be pushed back from Iraqi territory without any further changes of course by any faction; the Kurds, Iraqi government and Iraqi Shi'ite militias appear to be powerful enough to accomplish this with Western air support. This will reduce the war to Syria within the next two years, turning Iraq into a pro-Assad foreign power in the conflict. The Kurds will likely be able to realise an autonomy in Northeast Syria, tolerated by the Assad regime just as the Kurdish autonomy in Iraq is tolerated by the majority Shi'ite Iraqi government. A Turkish intervention against this enlargement of autonomous Kurdistan is unlikely.
Daesh will be cut off from reinforcements by Kurdish advances along the Turkish border, and will be doomed save for an unlikely Turkish intervention against the Kurds.
My guess is thus that this will reduce the conflict sooner or later to a clash between pro-Western and pro-Russian factions. Daesh may be eliminated before or after these two factions come to an agreement and it's likely not substantial which faction gets to gulp more of daesh territory if an agreement comes second.
The key question will remain the survival of the Assad regime. Russia is trusting only this regime to maintain Russia's privileged role in the country, and is thus unlikely to ever give it up (though Assad himself may be replaced by some other regime politician to save the West's face). The West is still stuck in its extremist views on war and war goals, and unlikely to give up its disproportionate demands any time soon. Maybe their Syrian proxy (the FSA) will under pressure of continued defeats in battle, though. The probably impending fall of Aleppo may produce a moment of willingness to accept a compromise.
The Western readiness to compromise on the Assad regime's survival may change after Obama is out of office, of course: The Western public is more focused on daesh than on the regime, so eliminating daesh as a territory-controlling faction may end up being enough and face-saving enough.
Assuming a power-sharing agreement under Assad as president, Western politicians could deflect all criticism concerning the survival of Assad by pointing at damage done to daesh. I suppose the vast majority of voters would be fine with this.
P.S.: It's interesting that the Western powers do not really protect the FSA, or harm regime forces directly: Any attempt to do so would be either opposed by or compensated for by Russian intervention. Meanwhile, the Russians do bomb the Western-aligned FSA at will. Putin obviously is more brazen and aggressive than the West, even in indirect confrontation with the West. The Turkish interference (the Su-24 shootdown affair etc.) may have served as a warning shot to draw a line, limiting Russian aggressiveness.
Furthermore, Russia has the advantage of intervening in support of the internationally recognised government (thus no aggression), whereas Western intervention against the same would be an aggression.