I can't say for sure what is the 'best' build, but one thing I've found that made the game much easier when I played it is having a very high chance to reflect projectiles. I built my vanquisher mostly like you, focusing a lot on ricochet and exploding shot, ranged damage, and critical hit and putting most points into dex, with some into other stats as needed for better gear. Basically I was a glass cannon, the only problem I had was survivability from ranged and magic attacks.
One thing that made my game exceedingly easy was to find a pretty low leveled shield with +20% or higher chance to reflect projectiles, and then enchanting it a few times. You need to get very lucky (and let the enchanting succeed 8-10 times without wiping the item). On top of that, what you want is to have the item to go over 100% chance to reflect ranged attacks. This, in effect, made you immune to all ranged attacks as well as magic (I'm not sure if this is currently still the case as I haven't played the game for a year). This made the Dark Zealots (and their insane damage magic attack) much easier to handle. All I had to do after getting that shield was to maintain my distance and kill everything with exploding shot.
Here are my observations:
Your projectile will only ricochet at most twice off of any objects that are not monsters. That includes walls, lamps and other doodads that you would expect shots would/could ricochet off of. The initial shot will go as far as it can until it hits a surface (or it leaves the screen, can't tell for sure). For each ricochet, the projectile will only last for a certain distance. I'd say the distance between you and the edge of the screen (when oriented "straight" and not in the isometric perspective).
Your shots actually go through monsters dealing damage based on your weapon(s) DPS and skill level of your ability. It does no damage to you or your allies whatsoever.
Using it can be somewhat difficult. Targeting a monster will not necessarily hit it, the path your projectile takes will always be in the direction of your cursor. It is more effective if you shoot toward a flat wall. Any irregularities on the surface will cause it to ricochet more essentially stopping it.
It is most effective if the monsters are lined up and you shoot straight through them all. Or, even more so if they are against a flat wall or in a corner. The additional ricochets will deal additional damage.
It is not so effective if there are many doodads on the ground (blocking your shots) or if you are surrounded out in the open.
Make sure you have plenty of mana potions ready or mana stealing weapons, using the ability can drain your mana pretty quick.
Best Answer
I remember those, no doubt it was tough every time.
First, let your pet draw their attention it will give you at least one free strike.
Second, use special skills to stun them, don't remember the name of the skill but it works.
Last but not least, be ready with potions no shame in using them. :)