I've had experance with DnD, ADnD, 4th edition World of Darkness as a human, mage, and vampire. The game I'm most intrested in right now is SCION.
/rant
WOD is the game I like least of those I mentioned. If I had to pick one thing that pisses me off most about WOD it would be the Morality system hands down. In DnD and many other games you can make the choice to be an evil PC or an apathetic PC who is on whatever quest the story is based around por personal reasons rather than because it is the right thing to do. Normaly the player needs to deal with the scoical responses form the NPCs as the only major recource to their actions, and I'm fine with that. WOD actively punishes the player for acting against the common western moral code. I have a habit of dealing with major baddies ond opisition in RPs by killing them once I get the chance in combat or out. In WOD if I were morality 7, the starting morality, and I got into a fight an assasin sent to kill me and I kill him in combat I'm fine, but if use a wepon of opertunity to knock him out or disable him and then kill him seconds later after combat has ended I have to roll for my morality. If beat the roll I make an excuse for myself and keep going fine. If I fail I drop to morality 6 and roll my new morality for psycological disorder. These start small and get worse at lower levels. They can never be removed, and they force the PC to act in a way dictated by their new instability. Some people might think this adds flavor to the PC, but if I have a full person in my mind and thy are put into situations that portray them in a negitive light and they drop morality I end up with new rules for how I can and can't act that are adverse to how I want to play! There is also the miscomunication with the storyteller to take into account also.
/rant
That said WOD is fairly simple to play and requires you to only know a few rules for making a PC and a few for actual play. It's simple, smooth, and fun if every one at the table in on the same page for the many 'gray' areas that they leave for the storyteller. You will need to know a second much more complacated set of rules if you want to play the addon games of Mage, Vampire, Werewolf, Promethean, or Changling.
SCION I only started into recently, and with my RP group spred along the coast for school my first hand experance is limited. There are a few things you need to know about SCION. The first is that it comes in three books named Hero, Demigod, and God. I have Hero and Demigod, but am holding off on God untill I can get a everyon's asses in gear of a few good hours of play. SCION in compared to Exalted a lot, and while I haven't played Exalted myself I'll take their work for it. You also need to know that SCION was put together with the intent that you could sit down and start play from the moment you bought the book. This is done by including one sample PC for each of the six pantheons, two histories for two of those six that the books follow, and one full story ready to be run though. Some people don't like that so much of the source books are filled with info that you don't need to actualy play, but I personaly feel that the back stories give the player a good feel for what a scion should be, and the prefab story can help a novice storyteller get the feel of how to run a game. The books themselves also have the habit of puting useful info throughout it's pages somewhat haphazerdly, and this translates to lots of stickynotes if you what to quick refrence a table or look up a rule that you are unsure of. I use two colors to help with figuring out where full sections are, and where the tidbits are. The combat system of SCION is also unusual in that by counting the seconds you can have two people acting at the same time. This leades to more rules that have to do with timing and how to use it to your advantage. The actual rolling of attacks is also a little weird in that it has six steps to add modifiers to the roll and seven steps in the order of attack. That migh seem daunting, but many are there to cover odd situations and standard defensive buffs like 'soak' that everyone has, while others are steps like "declare attack" and the like. One major difrence from WOD that I feel like pointing out is that when rolling to attack you need to roll first to hit using a dex roll before you roll to see how much you hurt your target. There are also rules you need to know for dealing with nameless NPCs and the like, but those exist to cut down combat time and to keep you from needing to roll thirty dice for a simple action.
High powered people are harder to put down than some people think because the combat system favors defence to attack, and you should take this into account when playing. The good in that is that your players can survive long enough get into it, but the downside is that if you throw in a 'boss' for them to fight that is too strong for them to kill in a timely manner you run the risk of accadently placing them in a fight that takes forever to finish. This becomes much more aparent in higher levels where someone can have a bashing soak, soak is subtracted from damage of that type before it is applied, of 22 and be in the middle of the meatshield pack. That is also assuming your strike gets past similer dodge dificulties.
Now SCION's overall feel is in a word epic and they say as much in the book. You are the child of god charged with a mission to help save the world and all of existance. If you want to get a better idea of what SCION is and how it plays you can go to the White Wolf page and download one mission, a basic set of rules, and a few PCs to play at the Hero level.
However! Before you buy the source books you need to know that any time any table that has been printed in Hero is mentioned in Demigod they give you the page number rather than reprint the table. Basicly if you want to play at the God level you need both Demigod and Hero books in addition to the God book. If you have played the example mission and are intrested but unsure I would recomend you stick to hero and just tell the other players to not powerlevel untill you are sure it is worth the money.