I like the 5e Ranger, both thematically (the best at this in any edition IMO) and in-vivo play. It is the absolute best class in the Exploration pillar of the game, and a well thought out ranger will absolutely crush it in exploration-heavy campaigns like OotA. That being said, it is a bit lacking in the combat department, although with a little optimization it can be brought up to snuff. I liked the latest UA subclass (Deep Stalker); it emphasizes the ambush aspect of the ranger, giving up a bit of DPR for a bit more Alpha striking capability (although, TBH, I am a bit biased towards since it favors the way I like to play), and the bonus spells known mitigate a major problem in that area.
Other fixes I would make would be:
- Make Hunter's Mark a Class Ability, and add extra damage if the target is a favored enemy.
- Detach Primeval Awareness from spellcasting, making it function more like the Paladin's Divine Sense.
- Fix the pet issue with a spell a-la Find Familiar/Steed. Make it a ritual for Rangers without needing to have the feat, and subsequent uses of the spell could be used to raise the pet when killed. A subclass or spells could be used to buff it.
- Like another poster said above, more flavorful/thematic spells that play to the Ranger's strengths.
- Somehow fix the level 20 capstone... it's not a bad ability, but not capstone worthy, either mechanically or thematically.