Glazunov completed his Fifth Symphony in B-flat Major Op. 55 "Heroic" in 1895. His own personal voice was well-established by this point - a synthesis of nationalistic and cosmopolitan influences, Tchaikovsky minus the pathos, Kuchka minus the parallel 5ths. This work, according to musicologist Richard Taruskin, had an out-sized influence on the first opus of one Igor Stravinsky (his skillful but hardly earth-shattering Symphony in Eb). The connection to subsequent work from a later composer (however much a stylistic dead-end) is the more fitting given the eclectic influences from earlier composers readily audible in Glazunov's Fifth. He rolls out the first movement's maetoso's broad introductory theme like a Wagnerian leitmotif, sounding more Rhein-maiden than Volga-boatman. The performance here is Valeri Polyansky with the Russian State Symphony Orchestra, from a great Brilliant Classics set:
This theme, along with many of Glazunov's harmonic twists throughout the movement, recalls Wagner quite a bit. Like basically every other composer from the last quarter of the 19th Century, he selectively infused his works with elements dutifully gleaned from the German composer, even though his own aesthetic temperament certainly did not line up with Wagner's. Following a lengthy slow intro, the first movement's sonata form gets underway with a first subject that speeds up and lyricizes that opening theme. The more dance-like second subject is a close relative to the first, and during the dramatic development section it becomes hard to tease apart which is guiding the way (especially given Glazunov's penchant for sounding them at the same time in invertible counterpoint).
If Wagner looms heavily over the first movement, then it is Mendelssohn dancing lightly that we hear when we move on to the second movement's Scherzo. The fleet-footed wind writing has Mendelssohn's elfin prints all over it, but the music is most appealing in how Glazunov's Russian rhythmic and harmonic sensibilities pucker the overall sound. (We can also hear the first of several, typically very innocuous motivic references to the first movement)
A different world entirely is presented by the Andante third movement. Two minutes of searching harmonies come before anything resembling a full theme is established:
These lush and dark progressions set a scene of nocturnal romance, but one continually threatened by outside forces. More than any specific musical similiarity, this tone of forbidden ardor is why I think some commentators have linked it with Tristan und Isolde. (The menacing, chromatic brass chorales that deter the lush harmonies at intervals contribute to the effect as well. But don't worry, the affair ends happily, in a radiant Eb-major, flanked on both ends by major third relations).
The final movement's vigorous and rhythmically jolting Allegro is pure Glazunov, seven minutes of sustained orchestral fireworks in a somewhat loose rondo structure, with 3 or 4 themes ripping past each other in quick succession. In it he manages to combine two of my favorite 19th century stylistic hallmarks -- beefy pedal points and head-scratching chromatic sequences. The second main thematic area combines both. It starts off with a threatening theme over Eb/D# pedal with a suggestion of 3+3+2 metrical subdivision. This gives way to a brief melancholic melody, still churning with unrest thanks to a constantly throbbing bass line. This is interrupted by the threatening theme once again, rearing its head in a more aggressive guise. The far-out sequence that concludes the section goes on for a bewilderingly long time, but still manages, in my professional opinion, to rock. 
Heck, here's the whole final movement, performed by the USSR State Orchestra under Evgeny Svetlanov. He breathes more fire into the finale, although there are some pretty weird tempi choices.
1: Taruskin, Stravinsky and the Russian Traditions Volume 1 (205-222)
2: Part of the ass-kicking nature of this sequence owes to the way Glazunov mixes major and minor third progressions, all the while navigating downwards by semitone -- this manages to make a progression that at its core might sound like a lessening of intensity, and increase or decrease its tension at Glazunov's orchestrational discretion.