Arguably, yes, though revolutions are never really as revolutionary as we like to imagine, and certainly I'd say the French revolution was the biggest turning point in this era. The legacy of 1789 had a huge influence on events in 1848 and thereafter.
A couple of points I would make:
The revolutions weren't a vital turning point everywhere. Older work may dismiss 1848 as a failure in every area but France. This is not true, but in plenty of places revolutions were either crushed completely, or fell far short of what they hoped to achieve.This was particularly true in areas where aspiring nationalist movements overlapped, conflicting with and compromising one another. This can be seen well in areas to the centre and East of Europe such as in the Austrian Habsburg empire, where the Habsburgs were able to play off competing nationalist movements against one another. Linked to this was the advantage of reactionary old regimes being able to use armies which were of a different nationalism to the region they were reconquering. Again Habsburgs used this technique (as well as Prussians in other parts of Germany); if an army was sent to subdue and kill their countrymen, the loyalty of the army was not assured (this was the problem in France), but if this was avoided, old regimes had a much better chance of reasserting their power. This is seen particularly well in Italy, where General Radetzky withdrew to the Quadrilateral Fortresses (I think), removed the Italian soldiers from his army, then reconquered the peninsula.
In other areas, Revolution turned to Reform, and so was consequential, if not a revolutionary turning point. This can be seen in the Netherlands and Belgium, where monarchs realised the direction events were taking, and submitted quickly (often fearing events of 1789 and thereafter in France). In such places, constitutions and other such concessions were achieved, which is significant, if not exactly a turning point.
In some places, 1848 set up important components for future events. In Piedmont and Prussia, liberal havens were created in 1848 which made these states the ideal breeding ground for nationalist and liberal ideas which would contribute to each country leading the unification of Italy and Germany respectively a decade or two down the line.
Just because change was achieved didn't mean it would stay. In some places, even when constitutions were granted, the liberal and democratic ideals which had spurred the revolutions was not evenly spread throughout the country, and so when rural peasants were offered a vote, they could be influenced by local nobles and clerics to vote for a reactionary representative. Thus, often revolutionary democracies elected conservative governments.
So, to answer your question, I'd essentially say no they weren't, but that does not mean they were outright failures. Looking for 'turning points' in history has always struck me as odd, since Historians are in the business of explaining how everything that happens was caused by something before, but of course some events have more consequences than others. Using this definition of a 'turning point', I'd certainly prefer to look back to the French Revolution during this era for the real 'turning point' which changed the game.
Hope this helps.
Sources: a lot of what I wrote can be found in 'Revolutionary Europe' by Sperber, but also in conversations I've had personally with Tim Blanning, one of the pre-eminent historians on this subject (he teaches me at university). Of course I wrote this late at night and without notes, so I am open to being corrected, just trying to help. Ta!