The purple worm is everything you'd expect of it. Enormous, strong, dumb, and almost unplayable thanks to HD.
Seriously: while 35 strength, 25 constitution, and gargantuan size sound nice, the fact that one needs to surrender 16 levels to get it is problematic. Add to this the abysmal intelligence and skill list all purple worms are cursed with, and even something as simple as entering a prestige class will be difficult.
Tremorsense, Poison, Improved Grab, and all that are neat, but outdated (and frankly, never all that good).
Rakshasas are next!