Ranger's identity should be tracking, herb lore*, nature, and self-sufficiency**; all on top of a basic fighter-like warrior chassis.
@Minigiant is on to something with natural sciences, to a point: meteorology, cartography, astronomy, basic medical knowledge for self and animals, and plant science: sure; but not geology (unless a Dwarf) and not social science. The player would select one or two of these sciences from a list during char-gen.
I'm of two minds as to whether Rangers should ever cast spells, but IMO at most spellcasting should be a very minor feature of the class - maybe no spells until 9th level then 1 spell a day (from a very short list and cast as if 8 levels lower) until 15th then two a day after that.
Along with Bards, Monks, and the other "life-style" classes, Rangers IMO should be highly restricted in their multiclassing options as well, even to the point of they just can't do it. You can't just dabble at Rangering; it has to be your life's focus to the exclusion of anything else as time-consuming as learning another class.
* - D&D has always had available, but never really used, great gobs of design space around magic or quasi-magic herbs and plants; and Rangers are the obvious class where this would fit.
** - as in, able to forage for itself and survive in the wild on its own; this doesn't extend to being able to forage for a whole party.