Bit of info first: Rebirth tier is increased if you rebirth while at the level cap of your current tier. (Sadly this makes enemies stronger while only providing a slight boost to your max level, which makes it quite unsatisfying to me. Essentially you're making everything harder for no real reward. It doesn't even boost the xp enemies give. Slight drop rate increase which seems to apply to equipment and souls, but... equipment is SUPER level capped and souls drop rate quickly becomes awful.)
Rebirth tier seems to function as a multiplier to how many rebirth points you get. The first rebirth offers no rebirth points (or maybe just 1? It's been a bit now).
Ascensions don't reset souls, so it's a good idea to go to higher zones if it allows you to farm up an extra souls tier if you plan on farming ascension shards. The drop rates get pretty bad though, so if it takes too long to get a higher soul tier then just begin resetting. You'll need to do it often anyway.
Over the weekend I've managed to amass 250 rebirth points by keeping this game open on the side while watching movies. And I've definitely come to the conclusion that the whole rebirth loop feels unsatisfying. It'd be a bit better if there were some form of skill tree point automation. It'd be even better if the game gave more than a pittance for rebirths. Ascension shards suffer the same fate, sadly.
On a more general note the game has issues with information. In ascension tier 2 there's an upgrade that says "Unlock Amulet[T1] Suffix", but this tells you nothing. What this actually ends up doing is increase level caps of the skill tree as well as add new skills.
When you get 25 rebirth points total you unlock "Open equipment T3 complect", what this actually means is that you now get a small set bonus for getting your equipment to tier 3. +3 min level, +3 max level. Also: please change "complect" to "set" or "equipment set". Complect is apparently a real word but its meaning does not fit, or at least none of the definitions I found fit.
Speaking of min level, it's a little bugged. Min level does NOT provide skill tree points but does count toward the level cap. So for every +min level you have you essentially lose the same amount of skill points (if you were to reach your level cap).
Buffs as a whole are alright, but they're definitely not made equal. And personally I'm not a fan of being unable to switch buffs without undergoing a reset.
First Strike feels useful from the start and massively helps with farming, but the Combo buff has me questioning what it's supposed to do. Combo gives a slight damage buff but it gets reset when you get hit, and "enemies can dodge attacks" is one of the basic curses so you'll lose that combo all the time. Even with the buff at level 3 you'll lose 50% stacks when you get hit, and 25% at level 4. Oh, and to the dev: it's supposed to be stacks, not stucks.
Coincidentally First Strike and Combo are also the only two offensive buffs I have at this time, so it's honestly quite painful for one of them to seemingly be incapable of working.
The Amulet tab unlocks at Stage 20, even though the actual amulet doesn't seem to do anything until after you buy the relevant Ascension upgrade. It's probably so you can see info on the curses, but then the first amulet tier should probably say "unlock with an ascension upgrade" or something. As for the curses, while the various tiers are listed on the Amulet page I have no idea what tier of curses an enemy has at any point. Am I still facing enemies with tier 1 curses? Or have we moved up to tier 3? Can an enemy have any tier of curse from the moment you unlock them? I have no idea.
Currently on stage 32 and making a push to stage 40 for next level of ascension upgrades but I doubt I'll get there. Zone kill requirements get ridiculous way too fast, as do enemies' stats. Honestly the game feels needlessly stingy with giving players growth options or rewards, it's to the point where I'm tempted to edit my save and just multiply my rebirth points by 10. A full weekend of resets shouldn't feel worthless, but in this case it largely does.