I've just finished all the quests that I can do, and I must say that I'm astounded that one guy has produced something of this quality. I have some criticisms, though.
My first criticism is that everything is crazy expensive for low level characters. The merchants rip you off to the point that it's not worth buying most things from them.
This means, perhaps most importantly, that PSI isn't economically viable at low levels due to the cost of replenishing it, unless you enjoy standing next to mindshrooms. The need to hang around mindshrooms after almost every kill introduces an element of tedium and makes the "Shroomhead" feat mandatory for a character using PSI. Inability to afford PSI vials effectively means you are limited to 40% of your maximum PSI all of the time.
It's not just PSI vials, though. Gear like grenades, to even the odds in the more difficult encounters, is prohibitively expensive. Most of the time, enemies come in groups, which is what makes encounters really difficult. Crafting requires a huge investment of skill points, to the detriment of basic combat ability, and low level characters simply won't find the required components anyway.
So, I think the game needs rebalancing for low level characters. Low end stuff to aid in combat should be easier to come by or available at correspondingly low prices from merchants. High end gear can remain suitably expensive.
My other criticism is that many encounters require tactics that I would deem to be meta-gaming. For example, when I met the bandit guys near the siphoner pools, I really had no chance of winning unless I used both entrances to the area to kite them and cause them to become strung out and split up. So I would enter by one entrance, do some damage to the nearest guy, leave, enter through the other entrance, do some damage, leave, and repeat. Between entrances I would go and stand next to a mindshroom for a while. Eventually I killed them all, but having to resort to meta-gaming seems indicative that balance is off.
Despite all that, I think this game is really cool and I hope it's going to get some more content in future (and maybe a balance pass!).
The early game used to be even more difficult - it had more enemies (rathounds) in the starter areas and they were a bit tougher and you also started with far less money. Since then I've been steadily making it easier on both fronts. It's still a bit off according to feedback I've been getting. Even though I personally don't have much trouble when I'm playing through it, I can understand how someone new to the game might. I'll probably add some more loot (meds, ammo, repair kits) to the early areas to make it a bit easier and to help people avoid having to retreat back to the base before finishing the first mission.
Pure PSI is not meant to be viable early game. You should still use your weapons relatively effectively at close range even if you decide not to spend any skill points on them. You need to be versatile early game, specialization comes later. Shroomhead will probably get changed in the next update to make it less tedious.
I'm currently considering restoring all the health to enemies upon leaving an area. I know it won't solve all the problems with this tactic, but it should limit it's effectiveness a bit. That said, the problem with the encounter you described (and other similar ones) is that it can deal a lot of ranged damage up front at the beginning of the combat from which it's very hard to recover. Hopefully when energy shields are implemented they will help greatly with this.