I didn't have any relevant images, so enjoy the new, pointier Orgrimmar!
I made a few level 1ers starting out including a Divine Bovine, so I can talk at least about the level 1 experience for leveling, in regards to Paladins (based on the knowledge of a level 5 and a level 80 paladin) in the new system. I have a level 3 warrior, but there's not too much new there insofar. I'll burn off a PTR Premade Warrior later tonight and investigate that.
LEVEL 1:Starting at level 1, everyone starts with only one active ability, so you basically got only one button to push. I've tried Paladin, Shaman, Warlock, Warrior and Mage, and their attack is Crusader's Strike (!), Lightning Bolt, Shadowbolt, Strike (New warrior power, 20 rage, 3 sec cooldown, instant cast: Does 52% weapon damage), and fireball respectively. I believe the new logic behind the game is, "Pushing buttons are fun, so lets have players do that more often in the beginning," and classes like Warrior rely MUCH less early on on auto attacks than they previously did.
The first ability you get is a level
3, accompanied by a small quest (generally cast this attack on a target dummy near the trainer x number of times) and from there it seems to differentiate between classes how your ability acquisition progression goes. For the shaman, it was about one power ever 3 levels, where as the paladin got 2 at level 3 (Seal of righteousness and judgement) and doesn't seem to get another until level 9.
The thing that interests me is the choices they made for which powers you get and when. For example, the first healing spell paladins get is at level 9, and works off of the holy charge system rather than mana (details in a minute). I quickly made a priest to look at their power progression (it can be read in your spellbook, I'll capture an image later for an example) and they don't get a healing power until level 6, which I find VERY odd for basically what is in general a healing class!
This may seem like less of a deal than expected, except for the changes to combat low level. Gone are the days of having an absurdly high spirit regen and more health / monsters that hit like malnourished butterflies. You won't pull the "in combat basically straight until level 10 without breaking a sweat" anymore. Combat at these levels feels more like combat at level 80 (before purples and raids, think mundane combat) with fewer buttons and in terms of how much health you have at the end of a fight. With the lower regen, and no heals, it means you generally have to take more breathers (unless you get some food to drop). Monsters too at lower levels have attacks that were generally saved for higher levels. Troggs can bat you backwards all Mighty Blow style. Boars can daze you for a moment. Level one combat can actually be dangerous if you don't pace yourself! You seem to level slower than the previous ramping up of leveling speeds before as well, almost like the original pacing, which makes sense since they want you to savor the new content rather than whizzing by it.
Probably the biggest thing you'll notice is in each starting area generally, you start out in a situation of combat surrounding you. For the Dwarven starting area, Troggs are literally constantly charging the landing where you spawn, trying to get into the city behind you. Think the entrance to Outland on the other side of the portal. The orc starting area didn't seem to have this, so there are a few exceptions (I'll discuss them later if desired). This is seen a lot more often throughout the world, including level 80 content (this is everywhere in Mt. Hyjal), so get used to seeing fights everywhere.
PALADINS:Let's talk about Holy Power. It feels less like rogue combo points to me as is the internet forum joke, and more like rogue combo points and Warrior's Rage (Or if you prefer for analogies, Rage's less attractive cousin Death Knight's Rune Power) went out on the town getting some drinks. Soon they were both smashed and unable to find their car keys, so they split the fare for a hotel (single bed to be thrifty.) The next morning, hung over and sick, they came to the realization that they both were not sure entirely what happened the night before, but were ashamed to find their underwear somehow made its way onto the ceiling fan. 9 months later, Holy Power was brought into the world.
As typed before, Paladins start with Crusader's Strike. This very well may end up being the most important Paladin power ever, since it seems to be the only one that grants Holy Power charges 100%. With talents, other powers like Exorcism, Judgement, etc can generate Holy Power, but only at a 40% chance (for Retadins, I haven't tried Holy or Prot yet so I don't know their mechanics.) Being the only power that grants it 100% and given the amount of abilities/ that either require Holy Power to use or benefit from using them in other ways (such as increased healing/damage percentages), Its assumed that EVERY Paladin is going to be using Crusader's Strike, and as often as possible in rotations.
It might be obvious to all, but Holy Power is something that you generally want to charge to full before executing a power that uses it. Example given, Retadins specifically have a new attack called Templar's Judgement. Instant Cast, no cooldown, Consumes Holy Power, and does weapon damage percentage based on how much holy power you have. one charge = 33% weapon damage, 2 charges = 115% weapon damage, 3 charges = 225% weapon damage.
In general, Paladins kinda feel more like Warriors than they did before, which might comfort Brett (at least Retadins.) I personally don't know how I feel about it yet, excited in some ways and disturbed in others. for example, through talents, Judgement becomes a big time fight-starter (one set of talents increases its range to 30 yards, another gives the paladin a 45% bonus to speed if cast on targets more than 15 yards away for a few seconds, one grants replenishment for mana, another grants a boost for attack speed, the last being actually a holy tree 1st tier talent.) It basically becomes JUDGEMENT CHARGE, which is awesome, and should make Brett more comfy playing as such.
More as the world turns. If you have specific questions that I did or didn't answer, please ask.
Edit: forgot a few things. level 9 paladin healing power is Word of Glory, instant cast no cooldown, heals target for 1627 (at level 80) per charge of Holy Power. Also, it seems like ranks of abilities are gone as well (No more 14 ranks of fireballs taking up two pages in the spellbook.) Not sure how abilities scale while leveling yet.