The Piano Concerto No. 2 by Rachmaninoff is a mainstay of the classical repertoire. But my own reasons for having a go at it might not be the same as those of other musicians. (I'm not a musicologist, of course, so take my thoughts on the music with a grain of salt.)
I get the sense that Rachmaninoff appeals to many pianists as something like a challenge. His pieces require tremendous piano technique. The movie "Shine" was about a troubled pianist and his struggle with the extremely demanding Rachmaninoff Piano Concerto No. 3. It's the Mount Everest of piano pieces, no doubt, and the Concerto No. 2 is not much easier.
I need to say that this aspect of the concerto is not what appeals to me. In fact, I love this music---you have to love it to be willing to spend the hundreds of hours I spent on it---but this is in spite of the virtuoso sorties.
What does draw me to the music is Rachmaninoff's unbelievable sense of melody. Melody is an aspect of music that I believe is quite undervalued by serious critics. It's just the fluff; who cares? When we talk about the very best classical composers, we tend not to talk much about the actual tunes they came up with.
So let us step back for a moment and admit, front and center, that Beethoven was not particularly strong on melodies. The "Ode to Joy" melody is well-known and beloved, but as a standalone piece of music, it's really not that great. Similar to "Twinkle Twinkle Little Star", say. The strength of the Ninth Symphony lies elsewhere. Now, instead of jumping immediately to the more "serious" musical aspects where Beethoven shines (and yes, there is much to talk about), I say we should also look closely at his melodies, and compare them in detail to melodies we find elsewhere.
So where do we find the best melodies in European classical music then? In my opinion, this is not a central part of the Germanic tradition at all, nor of the French, the Italian, or others. It is, however, a big part of the Russian tradition, Tchaikovsky and Rachmaninoff for sure, and others like Borodin and Rimsky-Korsakov too. It's no coincidence that these are the classical composers whose melodies have been mined by Tin Pan Alley composers and others for popular ballads.
(As an aside, it does take some practice to actually say anything negative about the very best classical composers, but to my mind, this is what critical evaluation is all about. Beethoven may be a champ of European classical music, but Tchaikovsky had better melodies, Ravel had better orchestration, Handel had better fugues, Chopin had better lyrical piano, etc. But where, and in what way? It's surprising how little of this sort of analysis we get from music critics and teachers!)
So here is what is interesting about the Rachmaninoff Piano Concerto No. 2 (in my opinion, of course): it has a fast first movement, a slow second movement, and a fast third movement, but each of these movements also contains a slow, breathtakingly beautiful melody. These three melodies are the core of the piece and what I really care about. They are each played a few times, but overall take up only a small fraction of the entire piece. As far as I'm concerned, the rest of the concerto, is just there for contrast and to prepare us to focus on those gems. If the art of melody is not your thing, the whole concerto is pretty much a write-off.
Just to be clear, the melody I'm talking about in the first movement is first played at 2:35 in my performance; in the second movement, it's at 1:01; and in the third movement, at 1:59. Obviously, there are a lot of other things going on in these movements. For one, there are other themes. The first movement starts with some dramatic chords and then jumps into a fast theme that sounds to me like a Russian work song (in the spirit of Tchaikovsky's Marche Slav, say). The third movement starts with a fast theme that sounds more military. (The use of the tuba and bass drum push in that direction.) The second movement has a striking rhythmic aspect, a wonderful 3-against-2 tension for a good part of it. (You can hear this most transparently in the theme that starts at 3:58.) There are also nice rhythmic effects in the other movements, and even a swing-like effect at 6:42 of the first movement.
What we mostly hear in these three movements, however, is a phrase of some sort that is drawn from the main melody or from some other theme, and which then mutates and evolves in repetition with different orchestrations, transpositions, emphases, and moods. This kind of theme development and variation is meat-and-potatoes in European classical music. Rachmaninoff may be better at it than Tchaikovsky, but neither hold a candle to Beethoven on that front. Maybe nobody does.
So what about those three melodies? The funny thing is that it is hard to say why they are so terrific. Other aspects of music are much easier to talk about: theme-and-variation, counterpoint, orchestration, dance rhythms, and so on. A melody might speak to the heart, but the head doesn't know what to make of it. Get out of classical music and ask yourself: Words aside, why is the melody to "Moon River" so much better than the one to "Jingle Bells"? It's tough to be clear. The harmonic structure is more interesting? There's more tension and release? Really? It's a bit like talking about humour. Once you say that there's incongruity of some sort, or that people of high stature are going to be pulled down a few notches, you seem to run out of things to say. (Maybe that's why comedy tends to get short shrift compared to tragedy.)
For my part, let me just say this. We would expect the slow movement of a concerto to have the melody that really matters. This is how it works for most classical composers (like the second movement in Mozart's Clarinet Concerto, or the Air in Bach's Orchestral Suite No. 3). The melody in the slow movement of this Rachmaninoff concerto is indeed gorgeous. It was adapted by Eric Carmen for his ballad "All by Myself" and with good reason.
The melody of the first movement is also a beaut, but what really speaks to me is the one from the third movement. I'm hard pressed to say what it is about that reprise on the piano pushing upward and the chords modulating to follow suit, but to me, this is genius of the highest order. I'm a big fan of melodies. I love Jerome Kern and Antonio Carlos Jobim. But this particular one would be my pick if I had to choose a single all-time favourite.
On the other hand, it is worth noting that the third movement is also the one that spends the most time on these virtuoso onslaughts: too many fast notes to no good end, in my book. Playing this movement live on a real piano must be like performing a quadruple loop in figure skating. The main concern is: can you land it? To me, this kind of thing is for the circus. I find parts of it unlistenable.
(Somewhat off topic, this is my beef with classical opera in musical terms: it has way too much of the circus in it. I would enjoy opera so much more if the singers were not expected to sing so high, so loud, and with so much vibrato. Leave the high seas for the sailors, I say, transpose the songs to a comfortable range, give the singers microphones so they don't have to shout over the orchestra, and train them to sing reliably on pitch without a lot of vibrato. Now then: let's hear what that music sounds like! And if you want to focus on the music alone, and not on the broader theatrical aspects, you can leave out the libretto too.)
So there you have it: a favourite piece of music, with my take on its strengths and weaknesses. No doubt an interpretation of this music by another performer will bring out the subtleties I have missed.