I find the ghost very useful even in the endgame. Depending on your character, it's nice to get healed up once in a while. Also, the heals of a high-level ghost are faster than most potion - and you get it totally for free (not that it matters later, but in the midgame, it saves you tons and tons of potions).
Actually, having a high-level ghost makes the endfights (mostly the one of ED) much, much easier to handle. Also, a ghost makes tight stuff as the fight against Raze, against the Power Rangers, or similar much easier. All in all, it is the skill I would recommend for any and every character to have as high as possible.
DKS took out some of the nastiest fights in ED but the ghost is still pretty handy to have in many situations.
Fear is worthless, imo.
Curse is "nice", but on normal difficulty surely not needed. Blind and charm can be turned into nice builds, but I found it annoying to have charmed enemies standing around when all "enemy enemies" are already dead (you have to wait for the charm to wear off to kill the charmies).
Blind is a handy thing, but it's not really necessary. Can make some things somewhat easier and itf fits for nearly any character.
Poison Arrow is nice, but not THAT nice. A ranger should rather out the skillpoints in something different and get more power of the ten skillpoints that you get in Poison Arrow. At the beginning (first ten or so levels) that skill actually helps somewhat. Given a ranger can easily dodge around in a distance vs. most enemies, this little help is not much needed, though.
Life Tap is the mana-regen-thing? It's awesome for characters that do not use much mana but have tons of life energy and a high life-regeneration. It's especially awesome to fill up your mana after summoning something or to be fresh again in mid-battle.
I think my ranger on the latest run did not drink more than a dozen mana-potions (and most of these in the early levels), so I could totally skip buying/making them.
Firewall is the pure blast, especially on a fighter. For a mage, it's really nice to have against larger groups (or around corners) and easily takes care of many enemies (especially if your fireball is again in cooldown).
The "Path of the Ranger" (the last thing of the rangers) the *THE* thing to have as a ranger. It turns your ranger into a war-machine that throws out 8.000 to 10.000 damage in criticals later on.
The ranger-bow-upgrade is also "nice", but you can live with only a few skillpoints in them for most of the game (throw in five points during the first 15 or 20 levels and you are good until FoV; if you then are swamped in skillpoints throw some more into it to maximise your damage-output).
I never felt I "needed" Potion Efficiency. If you need a higher health or mana output in a situation, just take the bigger potion and your are totally set. I'd not put more than one or two skillpoints into it.
Evade is nice to put one point in. The others really do not "pay" (10% chance to evade for the first, 2% for each following point). So I'd recommend putting that one point into it and be happy - if you want a higher evade, I'd use items.
