Almost every serious red spends time in barrel, which makes the question not whether oak is there but what it was asked to do. At its most obvious it lends vanilla, cedar, sweet spice and a firm tannic frame. At its most restrained it lends nothing you can name at all, and simply lets the wine breathe until the tannins soften and the fruit settles.
The species matters. American oak, long the signature of traditional Rioja, gives vanilla and coconut and announces itself. French oak is finer and quieter, which is why Bordeaux and the Rhône lean on it. So does the age of the barrel: a new one gives everything it has, an old foudre almost nothing but air.
Expect structure, depth and wines built to reward keeping. Cabernet and Tempranillo, Syrah and Sangiovese, Nebbiolo and Malbec all use the barrel to buy time.