I can't even say the name of this casting system without cringing, so let's just call it Alternate Casting. It's the counterpart to the nice, normal magic system that all the cool casters use, including the SUE himself, and so it sucks phenomenally.
Firstly, this is a broad, broad system, so it's awful at doing anything in particular. Warlocks and other eldritch casters use it, but so do psions, with some minor alterations, so the effects suffer from this BESM-style blandness that makes them sound utterly flavorless. I cast Bolt. Whee... Deadlands: Hell on Earth did this for the core junker powers just to make them easy to understand, and even they caught on to the monotony of it by the time they published the junker sourcebook. The SUE system "spell effects" are even free of side effects, material components, or XP costs. In short, they are the most boring, utilitarian, immersion-destroying schlock I've ever tried to get enthusiastic about using. But boredom I can handle.
What I can't handle is this idea that magic users need to be punished for casting spells. See, Vancian casting is apparently too arbitrary, so it gets replaced by an effectively random system. Casting spells inflicts you with fatigue when you fail a check. Too much fatigue, by which I mean two or three levels, and you run a serious risk of unconsciousness or death. For low-level casting, this makes it basically random; you might get twenty spells today, or you might get two. For high-level casting, though, the scaling goes totally out the window. You get a spell every fifteen minutes, because the ability to keep up with the check DC scales exponentially in cost as the DCs climb linearly and so the checks become impossible. Cast two, and you're down for a few hours, and soaking a -5 penalty to all actions meanwhile. (Great time for skill checks) Use metamagic, if metamagic is approved, and you're lucky to stay alive. Playing a caster class is an exercise in fervent prayer to Arenji (sound it out); it's not even a matter of preparation, just of sheer luck. But there have been some good systems with fundamentally luck-based magic.
Very few of them, to the best of my knowledge, make you buy individual caster levels of a spell. D&D, for example, has a lot of spells scale with caster level. Fireball is a great example; you get an additional 1d6 damage every caster level, so for one spell you can keep it around for a while. SUE system Alternate casting does away with this silly abstraction; you buy a 3d6 Fireball, then come back for a 4d6, 5d6, and so forth; there's no relation between them except for the need to buy the lower levels before the higher ones. Every time you do, the DC hikes up a little farther, the spell costs more XP to learn, and it's riskier to cast.
The other numerical effects don't change, either. They're constant for every spell. It's a damage spell effect? Great, it has 30 ft. default range. It doesn't matter who casts it, it has a 30 ft. range. It hits one target, etc. If you want to change any of this, go ahead and buy more spell effects and cast them simultaneously; perhaps a Range effect and a Radius effect. Of course, this level of customization drives the cast DC up immensely, and that's before metamagic, which as I recall has to be individually applied to everything it effects. For example, a spell with two variable numerical effects needs to be Maximized twice to have both of them maximized, and this doubles the metamagic DC.
And all this requires in-game weeks of research and "meditation" to begin to be able to achieve!
At least, that's the ideal.
In reality, the spell effects are always "too vague", and picking one will inevitably split it. This isn't the Lesser Lesser Greater ..., d&d-had-too-few-spells treadmill of arcane casting, but it's close; spell effects are split recursively until each individual one combines only with a specific tiny subset of the others -- and yet the maximum spell effect numbers never change, and of course alternate casting classes have a low limit of maximum spell effects known. Your average sorcerer can learn eight spells (by which I mean eight series of spell levels); three of them are needed to imitate, say, Charm Person or Fly, since Mass and Burst and Range and Duration are all additional spells, rather than metamagic effects or, I don't know, preset components of the effects. Not that casting them does anything.
I asked, just to pre-empt questions. Despite what the system would indicate, there is no Summon DM's Upraised Finger--and yet, whenever I cast it, it works anyway, and these magic rules are the proof.