Death Tier 1:
Unfortunately wither has been nerfed several times now and the current spell is pretty weak - the attack penalty is so small now that it doesnt make much of a difference - Ceresa can make better use of it but it's no good without several death shards. The strategic version bypasses resistance checks which is nice but the effect is still very minor. Another thing to remember is that this has no effect on magic based damage so mage units are totally unaffected by this.
Beserk feels too weak to me and I actually think its better not to cast it in 9/10 circumstances - poisoning your unit for a negligable attack bonus feels like a bad deal and it becomes unplayable on the harder settings where the AI's bonuses make each battle a slogfest. This spell is supposed to be the death opposite to regeneration but it really needs a boost.
Death Tier 2:
Blindness is a saving grace for death magic it's cheap and very effective IF it sticks - like all the curses it relies on spell mastery.
Curse is also pretty good too so Death2 is worth picking up.
Death Tier 3:
Antipathy has dropped in price from 100 to 30 which seems much better and I can see myself using this spell occasionally on the harder settings although the effect is pretty tame and I agree with Heavenfall that it should scale with further death shards.
Blood sigil, hmmm I like the concept however I think both beserk and wither need a boost, once these are improved then blood sigil will also benefit.
Drain life is the only lifegain spell in death and it feels weak to me - it's quite pricey and has a casting time and doesnt deal or gain much life either, especially if the spell is resisted - needs improvement or a cost reduction I think
Death Tier 4:
Mass curse is a nice upgrade to curse although I think they should also double the duration of it's effect to 6 turns as it's 2 tiers above curse and costs three times more mana so it should be a little more potent
Pit of madness is a great concept but I feel it should get a little bit extra as I currently opt for inspiration over this every time and really it should be the other way round as this is tier 4 and inspiration is available from turn 1. Minus 1 growth is a pretty hefty penalty that can sometimes completely stall growth in a city so what I propose is that in addition to the research benefit and cloak of fear, this spell also gives mana per essence too (i.e. it combines meditation with inspiration and the cloak effect but penalises growth)
Touch of entropy is expensive but does deal alot of damage and spawns a decent unit too - Ceresa is very good with this. I would like the lurk to be permanently gained and stick around after the battle too. This makes the spell more interesting and I feel Death magic needs some more nods towards the necromancer trope. How about giving the lurk the harbringer perk too?
Death Tier 5:
I currently don't bother with picking up death 5 even with Ceresa because there's nothing worth picking up from this tier.
I think bloodrage and all it's cousins are a total waste of mana - I know someone will pipe up and tell me it's a mana sink and isnt supposed to be any good but I don't accept that argument. This spell is a ) boring b ) so marginal as to be irrelevant.
Sacrifice generates more mana now which is good to see and given that population has limited impact (levelling up & tax) I can see myself using this sometimes. You could actually kill pretty much all the population once a city hits level 5 and just suffer a minor tax penalty so this spell can potentially generate alot of mana although it feels a bit cheesy to do this (you'd think the population would object to being sacrificed really).
Kill seems far too expensive to me - 300 mana plus skipping 2 turns makes this almost unplayable except maybe against uber bosses. If they make a resistance check you have wasted 3 turns and 300 mana for nothing, awful. Other cheaper spells get the job done for a fraction of the cost and the uber bosses have a good chance of resisting this spell - I would never use this spell in it's current form, ever.
Infection - a nice little spell though in practice I don't use it often
Corruption - this is excellent and helps to scale up all otherwise weak spells so that they become good - at 50 mana I feel it should auto upgrade the resource too though
Graveseal - excellent spell, the best curse of them all
Dirge of Ceresa - I think this has been the most nerfed spell and people are calling for it to be nerfed again - no more nerfing please as I'm often choosing horrific wail over her signature spell when playing Ceresa
Contagion - this has been nerfed really heavily too, I'm not sure if it's playable anymore as I haven't used it in a while
Horrific wail - this spell is good in the hands of a mage caster with a few levels under their belt - I'm hoping they don't nerf it but unfortunately any good death spell seems to be nerfed eventually
Soulburning - this is a good spell although it becomes overshadowed by flamedart at higher levels - I personally think this is fine as is
Syphon strength - a decent curse/buff - it feels fine as is