German-born Johann Wilhelm Wilms was mainly active in Amsterdam, where he established at the age of 19 and lived until his death. He is remembered principally for being the composer of what was used as the Dutch National Anthem from 1815 to 1932. His dates, 1772-1847, make him a near contemporary of Beethoven by birth (1775-1827) and a (less but still) near contemporary of Spohr by death (1784-1859). Those two "brackets" are significant. Wilms may have started his compositional activities under the influence of Haydn and Mozart, but these two late symphonies (and they are Wilm's last two), from 1819 and 1830, fully embrace the new aesthetics of the romantic sensibilities.
Comparing them with Beethoven's symphonies would be unfair to Wilms - such comparison would be unfair to any other contemporary composer, for that matter - but also stylistically inappropriate: there is much more full-blown romanticism in Wilms' style than in Beethoven's; those two symphonies are milestones on the path leading from Spohr to Schumann, really.
Defining precisely what it is that makes you immediately recognize that you are listening to romantic music rather than music from the classical era (that convoluted formulation, because it is not the same as "classical music"!) is way beyond my layman's capacities, although one recognizes it for sure and without the shadow of a doubt when one hears it. Tentatively, listening to Wilms and reminiscing on Haydn, Mozart and all those "minor" composers from the classical era that Concerto Köln served so well (Vanhal, Kraus, Kozeluch, Myslivecek and the likes), I'd say (other than all the harmonic reasons a musicologist would give): the powerful brass and timpani underpinning (I think the timps were rarely present in the orchestrations of the Classical era, and that it is Beethoven who really introduced them as one of the constitutive elements of the orchestra), the weight and impact of the basses, a vehemence in the violins that the "Sturm und Drang" style of the 1780s adumbrated but never approached, and, last but not least, the solo role ofen attributed to horn. There is no mistaking the melody first intoned by horn at 4:12 in the first movement of the 6th Symphony, then picked up by clarinet then flute, for anything a composer from the classical era could have written. There is an interesting stylistic ambiguity in the first minute of the slow and solemn introduction to that same 6th Symphony, but - as if Wilms was passing on to himself the relay baton from the style of his youth to the style of his future - at 1:11 it erupts strikingly: a rising interval of fourth intoned in full force by the brass, followed by a mighty brass choral underpinned by timpani, and you are meditating before the infinite vistas of untamed nature (the paintings of Caspar David Friedrich can't fail to come to mind; significantly, his dates are 1774 - 1840, REALLY contemporary with Wilms). The "Andante quasi allegretto e grazioso" of the same may start in a deceptively galant style and mild atmosphere, but soon powerful, rhythmically robust and Schumanesque utterances enter.
Don't expect Brahms either - we are not there yet. But these are magnificent works in their own style, representative perhaps of a time of stylistic transition (of which Spohr, Raff and maybe even Schumann in his symphonies would be other champions) but no less appealing because of that. There is great sweep, melodic invention, orchestral splendor. Endless gratitude to Concerto Köln for offering this new and invaluable discovery.