I played latest version for the first 24 maps of plutonia 2 on intermediate difficulty, ended up level 47, something like 3 hours of play in two sittings.
The combo bonus is so important (especially when the "chain" includes boss monsters) that the game quickly resolves into finding how to abuse it.
From earlier this year I had already seen how buying a "rune of plenty" is a cheap and guaranteed huge combo in big maps if you have a non-empty BFG. But very awkward to use the buy menu each time, so I didn't try this time.
First thing I learnt was improving STR until a single DB shot can kill most Doom2 monsters (from caco to hell knight), then make sure each shot kills one of them - or kills a zombi and wounds a larger demon.
Second was using the white aura, which ends up the only worthwhile one. I made the huge mistake of increasing it to level 2 (double the cost for no significant benefit), but still, around level 30 I started maximizing STR and ENERGY, and I could re-cast the aura when it was nearly empty, continuing a combo for many minutes (watch aura counter from time to time, count remaining seconds in my head) Combo counter doesn't reset on map start, so if you cast aura immediatley you can continue the chain! My biggest chain was in the 500s before I actually ran out of energy, and I gained 3 levels at a time.
I feel I've done everything I wanted to try with the combo system, and now it annoys me more than anything...
If I have a sugestion for a variant that I find much less a hassle, it would be a "bloodlust" skill/effect that scales player's (damage/speed/thoughness/whatever) according to a counter that increases whenever a blood splat appears (usually caused by player, but infighting and player wounds may count, why not?), and constantly reduces over time. : This "frenzy level" would increase when player is in active fighting, and slowly reduce to nothingness in a lull. Every single bullet would 'count', and the timing would be less "all-or-nothing" than the current combo game - where zombies and imps are the only ones that count until you reach unbalanced parts.
Generally, I find it a pity that you have put many new complex game elements, and yet I find not so many things to play with...
- Armors fill up the inventory over time : you only ever need the best one, but the game doesn't give you an option to clean (sell?) the rest.
- Health also fills up the inventory, though this might be a balance issue. Still, the total amount of items makes it impossible to select a "contextual use" item during fight: invuln when you're dying, radsuit if you accidentally fall in lava.
- exp gives points that you can put in a stat that gives your more exp... how does it make the game better than if it didn't exist :/ ?
- increasable player run speed : I put zero points, and was annoyed with the permanent rainbow bonus : faster player is harder to control precisely (shooting near pillars etc.) so this stat breaks the RPG rule 'bigger should be better, not worse'
- The cost of most/all auras too, as well as heal skill (higher level shouldn't have same or worse "effect divided by cost")
- increasing the damage by a huge factor makes ammo plentiful for bullets/shotgun. Soon, maps have many times what you need to kill all the monsters they contain. Cells have lesser effect due to bfg overkill, rockets I'm not sure because I killed myself a few times (self-damage scales?) and used them less. The game effects that speeds up the player animation doesn't have this problem, because you eat the same ammo to do the same damage.
What you've started with shields is interesting, though I didn't find an other shield until level 30. How about having some vary player speed (slow down but better defense) and mass (makes player less vulnerable to pushing, very useful on some tricky platforms where a fireball can push you to death : these give options that are interesting for specific places or maps. If you had one that protects from self-damage that would be nice too
rocket-jumper armor.
About health and armor, a simplification would be to make the pickups fill two counters on the player, medic supplies and armor materials, if the player is already at full health and fully repaired armor when he picks them. Then either a player command or automatic gradual effect would draw from these counters to perform healing and repair - how fast or efficiently could depend on skill.
The runes are nice though I don't understand all of them (Time stop oO), THEY are what the upgradable skills should be, selected and launched through the standard inventory system which is more handy than the skill menu...
