Echoes is worth getting if for no other reason than using the Screw Attack in 3D. (And it really kind of acts like the Space Jump as well.) That and all the extra morph ball stuff, including multiple boss fights done in ball form.
It's just that, overall, MP2 is the B- to Metroid Prime's A+ because the world-switching is tedious (especially with that annyoing animation) and even navigation within one world is pretty boring; the different areas aren't as intricately and carefully interwoven as they were in the original. You end up having to walk through areas over and over again more than you should just because there aren't multiple points of entrance and exist.
Not to mention that the enemies were more compelling in the original. The color-coded space pirates who could only be hurt by one type of beam were better than anything at all that MP2 has to offer, and didn't even have to resort to having absurd amounts of health to chip away at in order to feel "difficult." If I could compare the enemies in MP2 to the enemies in MP1 in any way, I'd say most of them are like the Chozo Ghosts: they're annoying because they're easy, but have high health and often have to be killed before you can leave the room.
...And by the way, I thought Majora's Mask was better than Ocarina of Time by an even larger margin than Metroid Prime was better than Echoes.