The first season of TNG, DS9 and VOY were not very memorable but all of their second seasons very pretty good IMO whereas ENT did not really get better in its second season.
But the main themes were running through the show since the very beginning: character development, especially the trust and respect that Archer and T'Pol develop for each other which was continued on a larger scale with Maxwell and Soval, with humans and Vulcans in Forge/Awakening/Kir'Shara ... and the troublesome relations with the Andorians which lead into the prelude to the Earth-Romulan War in the fourth season. Or in other terms, how very different people with different goals learn to trust each other and get along. Sounds pretty Trekkish to me.
It is hardly a coincidence that they put it the show in the 2150s, they have worked since the very beginning towards the big historical events of that time period, the war and foundation of the Federation.
The only structural error they did IMO was the third season, such an arc would have come later anyway with the Earth-Romulan War, but it was a studio decision and not favoured by B&B.