Depends on how you frame it. On the one hand it was absolutely successful because it really brought the point of the revolutions to the forefront for a number of countries (or at least regions)- France, Germany, Poland, Italy, and the Austrian Empire.

Nationalism in a number of these countries would play critical roles in setting up both of the world wars.

On the other hand the revolution in itself was swallowed within a year, and for the tens of thousands of deaths across Europe only secured an end to absolute monarchy in Denmark, an end to the serf system in Austria / Hungary, and brought a (final) end to the Capetian monarchy in France.

To be blunt, while the point of the revolution was largely unrealized, it's message was powerful.

TIME magazine ran an interesting infographic a few years ago that compared the 1848 revolutions to a wave of modern revolutions that unfortunately falls within the 20 year limit. If you're interested in reading about that you can find the infographic here. I'll do my best to summarize the portion that explains the 1848 revolutions...

What essentially doomed these revolutions was that as the wave progressed, the radical factions in these movements went beyond what people seemed to be comfortable with, which created backlash. Additionally, some of the stronger countries that weren't undergoing revolutionary fervor, such as Russia, were able to send troops to help keep their fellow monarchs on the throne and prevent an upset in the balance of power, as they did to Austria.

There's few easy answers to this. Rapport's 1848: Year of Revolution is the most comprehensive source that I'm familiar with personally.

He doesn't link it to any one answer but in general it was the resurgence of the old conservative order. The French revolts were in particular feared as they evoked thoughts of the Reign of Terror. In many cases some time after the revolts the conservative orders simply took power back. That's a vague answer, but there is no single specific answer I can give. In each country it was a different mechanism that eventually restored much of the old orders.

Further comments: There was a lot of infighting too. Infighting may be the single most unifying description of the Italian revolutions, which were badly torn between Republicans and Monarchists who were willing to keep some form of limited monarch as a unifying figure. Those splits in the left were found in each of the revolts, as well as nationalistic tensions in places like Hungary, were what ultimately killed many of the revolutions and allowed restoration of the old monarchies.

It's worth focusing here on the key word 'revolutions' - plural and with a considerable amount of infighting within each national scene. One major historical argument is that their simultaneity should not be explained in terms of common political aims but the economic crisis of 1845-47 in Europe (Spoerer and Berger). As such you're talking about multiple failures/successes with different standards of judging that.

There's a certain fundamental conflict at the heart of the 1848 revolutions which is a European-wide movement of liberal bourgeoisie demanding constitutional reform, and behind them peasantry and urban workers agitating social conflict, but at the same time the 'springtime of the peoples' nationalist aspect. Each social group probably had more in common with their counterparts in other nations, but the ideology of nationalism quickly led to conflict between them.

So you have the Hungarian desire to separate from the Habsburgs while at the same time Croats within Hungary try to force their own separatist movement to place themselves under Habsburg control. Or the initial leading role of the Pope in Italy as a hope for liberal reforms before he backs down.

It's also worth bearing in mind that a lot of the revolutions were essentially due to the Habsburgs being temporarily too weak to support their subordinate monarchies. Once the conservatives gained power again and the power of the Austrian military was brought to bear, it became partly just an asymmetry of military power.