It's an improvement! Definitely a bit fuller, and more dynamic. Strings at 4:09 sound less awkward. Better selection for the jingle for sure - still repeats a little flatly per-section outside of the intro, but it matters less because the sound of it is richer and less stilted, and the timbre/shape gets switched up a few times. "I finally got one thing to sound like I wanted!" - Ain't that a great feelin' though? Motivating.
Retouching old stuff is always difficult, in my experience. If you're doing it in the first place, chances are it's something that's stuck with you the whole time, both as something you love and something you feel is unsatisfying. It's been in your head, telling you that *it* is and should be exactly what it sounds like it is in its current state, rather than a living idea with greater potential. It can be hard to choose to sacrifice old charm for newfound beauty, and if you don't know going in how to achieve exactly what you want, making improvements at all can seem like it would be a fool's errand. But art is only "done" when all authors have settled for the last time, and there will always be room to improve it further still.
So, next tier of criticism:
The FM synth at 4:18 is rather simple, messy in the low end, not enough to fill out its section, and kind of unfitting with the overall palette. Given the more organic qualities of the other instruments, a straight-up harpsichord might work, with some understated sixteenth notes thrown in because I think that's what people do with harpsichords, and maybe some layered sound design in the low end with the same sort of impact you get from slamming down a low note on a piano. If it's intentionally set apart as less organic, I'm not sure what to offer, specifically...
It would probably help to know exactly how the boss fight you're picturing goes, and for what sort of game. It doesn't seem like an "epic" battle so much as tense and calculated, like you're being fought off effortlessly, even gracefully, and while you're not overwhelmed, even one misstep would be a disaster.
The whole thing sounds a bit incohesive from section to section, though it would make more sense if each one were a different attack phase. My usual cheap trick to tie things together is to just let instruments and melodies bleed across borders, but these seem somewhat deliberately separated. Maybe some ambient buildups/bridges would work.
… uhhh ear fatigue is setting in and my brain is getting tired, so I need to just dump thoughts less articulately.
Bass drum. Automate the high end for some less-flat reverby clicking? Replace its low end with a slightly longer bass at the start of each measure?
2:14, jingles perhaps too loud.
Offbeat section-capping impacts kind of hollow now. Scooped-out bass? Stereo width conflicts?
I remember it seeming like some spots had too much activity in some low-mid frequency range on my first listen, maybe even like there was overcompressed reverb or something. Ear fatigue is making it hard to distinguish though.
Well, again, keep doin' sound stuff ("just for five minutes" any time you go a while without an urge). Obviously, you are free to keep iterating on this, but don't get hung up on perfecting it at this point in time - it'll still be around to pick up, assuming you KEEP SAFE BACKUPS and nothing unusual happens. Suitable arrangement of letters for one last line to close this thing off!