I love this episode. While the first half kind of dragged a little, the second half was excellent. Football X-7 is one of Phineas and Ferb's best inventions, and the sport itself was used magnificently. It brought a lot of character development to Ferb, and all the other characters had their moment to shine. I found really cool how Ferb gets visited by his cousins that live in the UK. The Candace plot is pretty interesting, but exaggerated, as always. I do fell, however, that the Perry X Doof plot was really weak. Seeing Doof sick was funny, but flowed really slowly when compared to the football match.The song "How To Be A Lady" is good but a little annoying. Football X-7, on the other hand, is good and really, REALLY catchy.
In conclusion, even though it has it's faults, "My Fair Goalie" is one season 3 best episodes, and definitively worth a watch and re-watch.