We really enjoyed Julian Serrano at the Aria. We didn't try the paella, just feasted on tapas, all of which were super tasty. I would especially recommend:
-- oxtail (raba de toro)
-- Yellowtail
-- croquetas
-- charcuterie plate
-- padron peppers
We had a delicious wine from Spain's Ribera del Duero region that went perfectly with the food.
The only complaint was how fast everything came out -- we finally had to ask the server to slow down the orders (which they did). I always forget how fast Vegas service typically is.
A definite recommend!