Well, the radar kind of sets the play style. Aliens get an automatic radar so humans are essentially incapable of hiding. They are large, loud, and can't be on any surface but the ground. Also showing up on a radar that all enemies have essentially defines their play style, as well as the aliens'.
So, radar certainly adds to the game from that point of view. You may be talking about the helmet, however, which many people agree is overpowered. However, it is sort of the field-leveling tool of S2; humans get a massive boost to their power at S2, but in a way I sort of prefer having a helmet to having a pulse rifle or a flamer. Also, egg hunts would essentially be impossible without human radar (which is superior to alien radar, because distances to target are clearer and elevation is also present).
Human radar does seem to have a confusing feature, though; dead aliens or buildings that suddenly disappear (have died or been deconned or whatnot) don't always get off the radar instantly. I dunno if this is actually on purpose, but I've wasted time looking for an egg that I already destroyed, because I saw it with my eyes and only then looked at the radar to see if anything else was around. And it DOES show information in blips, so it's not quite pinpoint. It's most useful for finding eggs/the alien base (a mass of unmoving points) and catching an alien ambush (dretch on ceiling/goon around corner). So, if it were only for moving enemies it would essentially be useless. Given the radius that the helmet lets you see, and the speed of most aliens, seeing them approaching you does nothing except get you psychologically ready for an attack (if you were asleep camping at the turrets), but otherwise would be relatively pointless.
