Beat it last night, day 8.
Honestly, it does get better in the final 3 days IMO. Mainly in terms of level design, more varied fights, and bosses. The crazy siege of the entire fleet of ships is a hell of a thing, by any standards, and does make you feel like a one-man army.
The finale and the final boss sequence(s) are well done IMO, and a lot better than all the earlier bosses.
Sure, it's still nothing like a real NG game in terms of the details, but as an action fighting game, it goes out on a high note at least and has a satisfying conclusion for what it is.
Overall, I'd say that the back half of the game is a lot better than the front half. Of days 1-3, 1 and 3 are just mediocre, while day 2 in the desert is pretty horrible. Though both day 2 and day 8 waste a long section on a lifeless, dull "turret" that should have been straight out cut.
Game picks up with day 4, which does have nice variety. After that it's a lot of fun for all its flaws.
THing is, I can see the seeds of a great game here. Entirely besides the conscious decision to try and make it "accessible", I still feel the game was cut short due to a low budget.
You can see this by going into the ninja trials - some of the trials actually use stages imported from Ninja Gaiden 1 and 2. In this engine, they look fine; no reduction in detail or texture quality. But they're superior in detail, construction, and textures to most of the environments in NG3's campaign levels. So superior that it's actually ridiculous.
Given that DoA5's stages look pretty good so far, I don't think it's plausible that like every single good staff member left Team Ninja's art department. It's more and more looking like NG3 really got shafted on multiple levels.