The Contra 4 original soundtrack clearly took its influences from the chiptuned composed and quasi-orchestral offerings of Contras 1 and 3 respectively, and less from the balls-out heavy metal rock styling of Shattered Soldier. In that regard, I believe the use of synths here adds a crucial and familiar element to the proceedings, especially to some of the more melodic sections of the score.
This I completely agree with, the Contra 1 and 3 references are very obvious and awesome in Contra 4. But you can't listen to something like HEART BATTLE and not go, "...whoa."
It's not the synth that I have a problem with, it's that the tracks have been arranged too mellow, but without the far-reaching touch that would allow me to dive really deep into the arrangement and the melody.
It could have been an ambient/lounge chilaxation album with retro touches and that would surely have made me go "...whoa." (Even Shattered Soldier had "Relic of Moirai"!) Maybe this will grow on me... but it doesn't look too likely at this point.