Im curious about the flavor and texture of the wines Were they heavy / light?

As a general rule, wines from the Mediterranean areas were richer and fuller than those made in northern Europe. This was largely due to climate. As you travel north it becomes harder to fully ripen grapes.

There were also regional tastes. The English for example were extremely fond of a light pink wine from Bordeaux called "claret". Customers in the low countries preferred richer and heavier wines. Wealthy wine drinkers in northern Europe also enjoyed dessert type wine imported from the Mediterranean area made from dried grapes. The very poor would drink thin wines made re-watering pressed fermented wine grapes. This "wine" would have been quite sharp and thin tasting.

Was white wine an option?

Absolutely. Especially in northern Europe (from Burgundy northwards) white wine was highly esteemed. White wines from Champagne, The Chablis region of Burgundy and the wines from Germany were considered great.

Was it frequently watered down

This varied depending on context, but the average person drinking an average wine would probably have it watered down some. Drunkeness was considered bad form.

or mixed with flavor additives?

Wine was frequently sweetened with honey and mulled with spices . Flavorings were frequently used to make thin and sour wine taste better so if someone had access to fresh and flavorful wine there would less motivation to try and "fix" it. Wine was also considered medicinal so herbs were added in that context as well. And even if you had good wine that didn't need improvement there clearly was a taste for flavored wine. For example we have a record of an expensive dinner made in 1379 for Parisian lawyers that included spiced wine. They could probably afford any wine they wanted yet included some flavored wines in their event (but also served some dry wines). The flavored wine was a popular concoction called Hippocras.

Here is one medival recepie for Hippocras:

To make Ypocrasse for lords [use] gynger, synamon, and graynes sugour, and turefoll: and for comyn pepull ginger, canell, longe peper, and claryffyed hony . . . Fyrst do in to a basen a gallon of redwyne . . . then put in your pouders.

TLDR: There was a variety of wine styles consumed. Those who could afford whatever they wanted would drink a variety of different types which was a testament to lots of wine being available and sought after.

EDIT: clarified the production of "piquette" which is re-watered grape skins.