So I'm about roughly halfway through the game at this point and put a pretty large amount of points into Poison bullets for range weapons. Noticed that death was pretty common before, but now combined with HP per hit and poison damage buffs, I am an unstoppable killing machine with a constant stream of HP coming my way.

Anyone else noticed this being a bit cheesy? Maybe the game gets harder from here? I'm at the Old Town part now.

You could be right, but I can't test it with my current character. The issue for me is that the best crit strategy is to keep the rage bar capped and pump the passives, and the poison DPS without rage is roughly zero. So while individual poison ticks can crit, the best way to use crits isn't with poison.

I primarily use poison for the defensive debuff, but the damage numbers for rage-boosted poison sound good. The only issue is that you can only refresh the duration. For large groups, you have to kite and you probably weren't focusing fire a whole lot anyway, but single-target DPS could be improved with other skills. Like those big guys with the cannons - you have to freeze them and kill them ASAP.

It may also depend on difficulty mode. Rage and other on-kill bonuses are harder to come by the more you increase the difficulty...