I converted and ran Axe not long ago. I'm not sure what railroading Whisper is referring to, the main adventure is a great big dungeon crawl. There is a riddle that could be construed as the "right" way to proceed through the dungeon, but it's really just the fastest/easiest way. Radruundar is a huge interconnected dungeon.
Actually, I think the riddle's greatest failure is that it does not reveal to the DM what the passages mean. Reading the adventure from cover to cover does not necessarily make the passages clear either, it requires that the DM plot a course from point A to B to C and figure out which passages then key to which areas. I went ahead and used the riddle, but I suspect the adventure may have been better without it. As my players pointed out right away, why would they follow a riddle to the hiding place of the Axe if all the ruckus was about the Axe being already unearthed?
One neat thing about Axe is that it's a book where you can see the mechanics that became 3E in the works. In order to make goblins challenging opponents for a high-level party, Skip Williams introduced some things like squad attacks, grapples and repeating crossbows. The maps of the Radruundar dungeon complex was also featured in WotC's Map a Week early on, in December 2000. Because it was a softcover and mainly a dungeon crawl, it wasn't as popular as the more immersive Tomes boxed sets, and often gets overlooked.