Well, there hasn't been any real discussion about animal companions and I think it's one of those gameplay mechanics that needs a lot of polish.
Lets start with what we know:
Rangers and their animal companions share their health and endurance pool.
Animal companions have their own stats (accuracy, damage, action speed, deflection, reflex, fortitude, will, damage threshold and damage resistance), most of them increase by 3 every level without anything other than talents influencing them (I may be wrong here)
Each animal companion has a unique bonus
Lets have a look at some gameplay scenarios
The brainless strategy: you send your animal companion into combat and you both die like flies in a matter of seconds (like using a wizard as a front liner, but even a wizard could survive longer with the right gear)
Conclusion: Suicide most of the time
Somewhat more strategic: The ranger starts shooting from the back line while the front liners engage the enemy. You send your animal companion in after lets say the 2nd hit trying to make it go around and target an enemy from the back to make good use of Stalker's Link or even knock down a spell caster and interrupt the spell.
Conclusion: A lot of micromanagement for little to no benefit.
Being cautious: The ranger and the animal companion both stay back. The ranger is shooting while the animal companion is just waiting for something to come and attack them providing some support and additional damage to finish it off quickly. Staying together may be dangerous tho. An AOE spell may hit both and Defensive Bond may help lower the damage by one category at best still taking a lot of damage due to both being hit.
Conclusion: Not much benefit from not sending your animal companion in and risk of taking ~1.5x damage.
I could come up with a lot more but the conclusion would be very similar: the animal companion seems more of a nuisance. The main issue I see is the lack of customization. All animal companions are very much the same, even the bear with its +3 DT and +15% DR. Lets have a look at the possible solutions.
Solution 1: Have the ranger and the animal companion have their separate health pool.
Personally I like the way it is right now and would look for some other solution, but it's a start. Of course the animal companion would still die like a fly, but at least it wouldn't take the ranger with it.
Solution 2: Lets increase this "strong spiritual connection" and let the animal companion benefit from the ranger's stats (attribute bonuses/maluses and equipment bonuses) that make sense to be shared.
I don't expect 100% of everything, maybe even 50% would suffice. I haven't done any calculations here.
Solution 3: 2 equipment slots for the animal companion with animal specific gear.
It doesn't have to be anything major and it doesn't have to be visible either. I'm sure some of you would like to see an armored wolf while others wouldn't like the idea at all. On top of that it's a lot of extra work for the devs. A good example would be the mabari war paint and collar from DA:O.
The TL;DR version
You can't adjust the animal companion to your play style due to lack of customization. The fixed bonuses gained per level just don't cut it and the animal companion ends up being more trouble than it is worth.
Feel free to discuss!