Hi, so I've just started playing as a priest, got into the town. Questing about.

Thing is on top of how spells and actions seem hilariously underpowered (takes like 8-12 spell shots to kill anything. more for stabbing) it seems like unless I use my limited use marks that normal spells are bloody useless as they fail 19/20 times. I can't find anything in the manual telling me why I can't cast for crap so could any of you tell me?

All I get is "Spell failure X%" which is insanely unhelpful.

You could try to go with seals instead of spells in the beginnings and wait for a few level-ups to distribute more points into Intelligence and the particular school of magic.

I haven't made it that far into the game yet, but after having fought a few different enemies with mostly spells it seems that I get different "spell failure" rates with different monsters.
For example, it seems that my spells seem to "succeed" 4/5 of the times against some zombies and bats, while against certain types spiders (not all) they'll "fail" 4/5 of the time and I can barely hit them.

So it does seem "spell failure" isn't entirely due to your stats, and also depends on some form of resistance from the enemy, as it seems success rates differ between enemies.

On the other hand, as Kovi mentioned. It seems that seals don't fail (or at least I haven't noticed them fail), so having some around to use against enemies you can't hit effectively yet seems to help a lot.

Intelligence gives spell resistance, so I'd say monsters with hight intelligence will be more resistant to spells than others.

I tend to build up my characters in rpg's with the more mundane stuff 1st, so after creating a Priest, instead on concentrating on spells at the beginning, I decided to put a few points into strength, armor, holy aura, flagellantism, and melee in order to be able to wield some basic weapons and have some durability, and because you can't be a disciple in spells until you reach lvl 15 anyway. So far I have not encountered anything that has been too difficult to kill, and have not had to deal with the frustration of early level spell failure. That being said, as annoying as spell failures must be, (to me) it still seems more forgiving than the level 1-2 Baldur's Gate mages. Remember casting your 1 magic missile for 3 points damage, and going thru your whole supply of bullets with your sling trying to hit one goblin? -- then have to rest (and pray you don't get ambushed) so you can repeat the whole process again?

Ah, I remember that when I tried the game. Lame shot at trying to be a "challenging" game.

Um, what? They were just following the AD&D rules.

I'm aware of that but it just felt forced. What's the point of using up 20 bolts or arrows only to miss 19/20 of them?

Ask whoever designed the ruleset, not those who implemented it :-P But yeah, beginnings are horrible in AD&D. It gets much better later on (or you can start with BG2 right away when you get a decently levelled character right from the start. You don't have to worry about such things then.)

PS support spells never fail

The feeling of progression? Once you put some more statpoints in dexterity and you see your hit ratio go up, you feel that that character is becoming better?

If you created a mage and put most points in intelligence, and they only had like 12 in dex, they're bound to suck with ranged weapons. In D&D, that's indeed a bit of a thing with mages: at first, they kinda feel like luggage you're carrying around instead of helpful party members, but once they start levelling up, their spells become devastating.

I remember running about with my Mage in BG, at least I had people to cover me in the early game. Took forever to find a meatshield in this one. And he mostly just out damages me and chugs potions.

As to seals, man I use them like crazy. The problem is it costs about 200-300 gold for a decent seal which has at most 30 shots. Weak ones take like 8 to down one walking corpse and even the fireballs take like 3.

So as to intelligence and points in magic skills, how much do you need for the success to be reasonable? I have like 40 something in intelligence (kinda massed on that stat) and 6 or so in Inquisitor magic. Mostly as I only have 2 damage spells and Open wounds seems to be the most useful.

That depends on what qualifies as "reasonable".

Again, from what I've seen so far, success rate against certain enemies can differ a lot, even if they look similar.
Some enemies are going to be pretty easy to "hit" while others seem to have such a high resistance that they're probably going to stay difficult to hit "under your own power" so to speak for quite some time.

I have similar stats but not as much Intelligence (I think I have around 30 or so intelligence). I use some seals, but so far not enough for it to be a significant cash sink.

So far I haven't had enough trouble against walking corpses for them to be worth using seals on. Maybe open wound will miss part of the time, but the walking corpses are slow and you can run circles around them so you have so much opportunity to "hit" it really doesn't matter as much. Bats and weaker spiders are the same way right now, Open Wound seems to be sufficient for them most of the time.
However, right now there are certain spiders with a different color pattern that I've been using seals a lot for, as they seem to cause a lot of spell failure. These are the ones I've been saving seals for at the moment.