Correct.
Runes are generally buffs compared to not using a rune. Some runes may add utility instead of just increase power. Runes change the way a skill works in some way, in its simplest form you basically just get a bunch more damage (and the graphics of the spell/attack changes to some extent.) Other runes may freeze enemies, add life leech or a knockback, or do something else. It differs from skill to skill.
The mage's hydra skill is a great example of this, the first hydra you get is just plain ole fire damage. Runes then change the hydra into lightning hydra that shoots bolts that hit instantly which is good for fast-moving opponents, arcane hydra that shoots relatively slow projectiles that explode and do splash area damage, or poison hydra that creates puddles that greatly damages enemies that stand in them, or ice hydra that shoots cones of cold that slows enemies and so on.
When you are first awarded a skill you have no runes available for it, you have to gain a couple levels first before they start unlocking. You gain your last skill at level 30 I believe, but runes continue to unlock all the way up to 60, so you must cap out first before you get to try out all of the runes...
The rune system is actually pretty cool, and adds a lot of fun IMO. Only "problem" with it other than not being able to pick the order they're awarded in is that many skills have more than one rune that I really really like, but you may only use one rune at a time (and you can't select the same skill + different rune in more than one skill slot), so sometimes it is very hard to choose which rune to use.
Also, when you hit the level cap the game resets your nephalem power (basically more magic find%) if you change your runes/skills, which I think rather sucks, but whateva.
D3 is actually very very enjoyable for quite a while IMO, at the very least all the way through the initial run through normal difficulty and perhaps all the way up to/through inferno, depending on how much of a fan you are of the genre. D3 is extremely slick, with very very high production values, graphics look great, music is great, effects, sounds, etc are great, the classes play well and are fun and so on.
It's only after a while that the limitations of the game design become grating IMO, but by then you have probably already had your money's worth and hopefully more from the game.
