It depends what kind of tapas bar you go to and what type of traditions it holds. Tapas traditionally used to be as simple as serving an olive on top of a bottle to keep the flies out. In time things progressed and became more exquisite.
I haven't been to Madrid so can't comment but I would highly recommend the inland cities, in particularly Granada, Arcos and Jerez de la Frontera.
The tapas bars in Granada work work on a kind of loyalty system: buy a nice glass of Rioja and you'll get a small plate of tapas, maybe a bocadillo or some tasty albondigas. Buy another drink and another and the quality of the tapas just keeps on getting better and better, culminating in a truly wonderful night out.
Having said that the majority of the bars overrun with British scum generally
won't serve good tapas, for obvious reasons.
If you find a good one, expect all sorts of delights, such as bacalao (fried fish), gambas pil pil (spicy prawns) olives, anchovies, bocadillos (small meaty baguette sandwiches), albondigas (paprika-spiced meatballs in thick smoky sauce), dry cured meats, pimientos, small rolled steaks, tomato and garlic salads, potatas bravas (delectable), the list goes on. Keep drinking, keep eating, keep smiling..

Enjoy!
