It's certainly less "in-depth" than Rondo - very few alternate exits, for example. As far as improvements or difficulty changes go:
-The crumbling bridge is in stage 2, not the next-to-last. Instead of being chased by bats, you are harrassed by severely inopportune fishmen.
-I love the Dogether and all, but Cerberus is actually somewhat of a challenging boss (at first).
-The Shaft standin certainly is no Shaft, but it's a really cool and creative boss fight. Yoiu have to be on your toes, or he will wreck you.
-Bosses in general are less susceptible to "stand in place and spam until he dies."
-They made the Giant Bat intimidating. Hit him at the wrong time, get swarmed.
-Using the key to free Maria and Annette is now much tougher. You have to keep that Key through a pretty good chunk of gameplay, including a NASTY platforming segment (fail and go to an alternate level) and the Dullahan boss fight.
-The sinking temple stage is very tough. Good use of water skulls, and the "sinking" part of the stage is nerve-wracking.
-Better graphics for the burning village.
-Fighting Death on top of the clock tower face is MUCH cooler than fighting him on a boring old pirate ship. The battle is essentially the same, althoughg he loses his background-to-foreground skulls (since the clock face is in the background, he would have had to shoot through it).
-There is one specific platforming moment in the last stage that will have you tearing your hair out, old school-CV-style. Two moving paltforms, medusa heads, and an angry axe armor at the end. SO simple, yet so hard not to fail.
-The Dracula battle is much improved in difficulty. Why? Because now it's platforming hell! if you don't choose your positioning wisely, you will die. T he axe is also now the best weapon for this fight.
-Dracula's second form is not as cool as his second form in Rondo, but it's a little harder to deal with partly due to the platforms and partly his slightly different movement patterns (he flies forward, and moves more than the old one jumped).
There you go! I do prefer Rondo of Blood overall, but Dracula X has some definite good points.