Based on my not-exactly-thorough experience with Neo! (I got to ST5 Boss @ Normal mode a few times), I'd say that what you see is what you get: a fun & unique scoring with, uh, serviceable level and boss design, I guess. It's been a while, but I don't remember the boss/level design being particularly great or bad, just okay. There's some occasional "enviromental obstacle" kind of stuff if you have a hard-on for that, but definitely don't expect R-Type/Gradius out of it. The fun's more in figuring out how to rake in the cash, and then what cards (special weapons you buy from the shops) to buy and where to use them to rake in the SCOAR (if you like seeing lots of bullets turn into shinies, you might like this game). Oh, and, of course, wrecking shit with some of the special weapons (like the GIANT FIREBALL) is its own fun
Fair warning, I seem to remember the 3rd and 4th bosses having some RNG stuff that can make them a bit tedious, and that some amount of boss milking is part of the scoring. I don't know what all bosses you milk, but I at least remember watching a leaderboard replay where the guy piled up bullets on the first boss for several minutes before moving on. (You also, technically, to an extent, milk a lot of the regular enemies)