It's still a dimension with no gravity and no "up or down".You can move while incapacitated. You just can't take actions or reactions.
If the entire target is suspended, then the spell would have to have an additional effect for the target to still feel g-forces (which I assume is what you mean by "under the effect of gravity"). If you rule that only part of the target is suspended then the target will definitely feel g-forces, but I'm hard-pressed to see anything in the description that suggests it's only a partial suspension.
I also don't see why it matters nor do I care.
In my game being levitated doesn't impose penalties or bonuses to be hit because that's not in the rule description. So I view it similar to floating in water I guess, exception that you can't "push off" the air enough to gain momentum and your movements aren't slowed.
Other than floating in the air, you are as stable as if standing on the ground in games I run. Because magic.