If you are looking for a really good introduction to the Gospels, look no further than the newly revised (second) edition of Mark Allan Powell’s Fortress Introduction to the Gospels (Oct 2019).
Powell is an incredibly talented textbook writer; this Gospels introduction is short (~200 pages), but offers insightful analysis of the composition of each of the Gospels and their unique features. He also comments on the production of “other” gospels. I spent a lot of time with the first edition as I was crafting my seminary course on Jesus and the Gospels. Highly Recommended!