What a great question! The short version is: the Baptist intellectual tradition is far richer than most Baptists (let alone non-Baptists!) know, and the fact that Spurgeon is the first name that surfaces says more about how we've told our own story than about the actual depth of the tradition.

Go back to the seventeenth century, where the real foundation is. John Bunyan is the obvious name, and people consistently underestimate him because Pilgrim's Progress has become devotional furniture, the kind of book that sits on a shelf and gets quoted in funeral sermons. But Bunyan was a serious theological mind. His Doctrine of Law and Grace Unfolded (1659) is a rigorous treatment of covenant theology, and The Holy War (1682) is in reality a more sophisticated allegory than Pilgrim's Progress even if it never got the same readership. Then there's Thomas Grantham, who I mentioned in passing with the Orthodox Creed context. His Christianismus Primitivus (1678) is a systematic theology, a full one, written by a man who had no university education and yet was petitioning King Charles II on behalf of Baptist liberties while simultaneously constructing a theological system. That combination of practical activism and intellectual labor is pretty characteristic of the early Baptist movement.

John Gill deserves his own paragraph, no question. He's polarizing, and some of the criticism is fair, but his Body of Divinity (1769) and his nine-volume Exposition of the Old and New Testaments are monuments of Baptist scholarship. The exposition took him decades. He pastored Horsley Down in Southwark for over fifty years, the same congregation Spurgeon would later lead as Metropolitan Tabernacle, and he was reading Hebrew, Greek, Aramaic, and interacting with rabbinic sources at a level that embarrasses a lot of modern scholarship. Andrew Fuller is the other giant of the eighteenth century and in some ways the more historically consequential one. His Gospel Worthy of All Acceptation (1785) essentially broke the back of hyper-Calvinism in English Baptist life and opened the theological door for William Carey and the modern missions movement. You cannot understand the founding of the Baptist Missionary Society in 1792 without Fuller. He was the intellectual engine behind it.

The nineteenth century gives you Spurgeon, yeah, but also John A. Broadus, whose On the Preparation and Delivery of Sermons (1870) shaped homiletical education in America for over a century and is still worth reading. And E.Y. Mullins, whose The Axioms of Religion (1908) is a serious attempt to articulate a Baptist theological vision on philosophical grounds, engaging William James and the broader pragmatist milieu. Mullins was president of Southern Seminary and had a hand in shaping the 1925 Baptist Faith and Message. His concept of "soul competency" has been contested ever since, which is itself a sign that it was doing real theological work. Also in this period, A.H. Strong's Systematic Theology (three volumes, 1907 edition being the standard) was the dominant Baptist systematic in American seminaries for decades. It's not light reading, but it's serious scholarship.

The twentieth century is where things get both richer and more complicated. You have W.T. Conner at Southwestern, whose Christian Doctrine (1937) was widely used and is underappreciated today. Then there's George Eldon Ladd at Fuller Seminary, a Baptist, whose A Theology of the New Testament (1974) is still a standard academic text in evangelical New Testament scholarship. Ladd's work on the kingdom of God genuinely shaped the field. And on the more constructive theology side, Stanley Grenz was doing serious systematic work right up until his untimely death in 2005, his Theology for the Community of God being the most accessible entry point. More recently, Tom Schreiner at Southern has produced substantial scholarly work in Pauline theology and New Testament introduction that gets cited well outside Baptist circles. Malcolm Yarnell at Southwestern, who has had such a huge impact on me personally, has (following the tradition of James Leo Garrett) published two of three volumes in his Theology for Every Person series.

For reading, if I were putting together a starter list: Fuller's Gospel Worthy of All Acceptation first, because it's historically pivotal and not that long. Then Gill's Body of Divinity if you want to understand the high-water mark of classical Baptist Calvinism. Ladd's A Theology of the New Testament if you're serious about biblical theology. And for sheer historical grounding, Tom Nettles's The Baptists: Key People Involved in Forming a Baptist Identity (three volumes) is the best overview of Baptist intellectual and theological history in print. Nettles is thorough and sympathetic without being hagiographic. That series will fill in a lot of the blanks you mentioned from your college days.

The tradition is there. It just hasn't always been good at publicizing itself!