Elements of Magic is not BESM. It is a totally separate / different d20 sourcebook.
Source books, actually, as there are two books on point based system and one on a skill based system.
Personally, I like both - far and above the slot system, but I think a synthesis of the two might work better. I'm working on a few ideas, but it will likely be a while before there is anything to playtest. The general idea is that magic would use Complex Skill Checks (sort of like what is defined in the UA; ie: multiple skill checks for a single success). Failures and (to a far lesser extent) Near Failures would drain the mana points, eventually bringing about fatigue, exhaustion, etc - rather like major draining of wound points (another house rule). Success by less than a certain amount (and failures by any amount) would increase the DC for all other castings until a period dependent on how difficult / complex the spell was.
In any case, as I mentioned it will be a while before I finish anything, but I have hopes that the system will work.
Skill based magic has its own difficulties that have to be considered, of course. Unless there is something to increase the DC over time (either temporarily or until the next full period of rest, etc) then it becomes little better than a warlock magic system (ie: infinite casting). While in combat situations that can be managed by lowering overall effectiveness, it does not work so well outside of combat. For example, being able to heal 1 hp at will is of little aid in combat - especially beyond first or second level, but being able to heal 20 hp at will is significant even at high levels. Similarly, dealing 1d10 dmg at will is powerful at low levels but of little worth at high levels, while 10d10 at will is too powerful at nearly any level except pre-epic (and sometimes even then).
Generally, you have to find a balance, an advancement rate quite different from what you are typically used to in normal 3.5e D&D. I would also suggest using 2d10 instead of 1d20, as otherwise even the most skilled wizard will fail on even the simplest spells at least 5% of the time. With 2d10 there is very little chance of failing on such trivial spells (and also very little chance of success on spells way beyond their current level) - thus keeping the feel of the wizard as being near or about a certain level, rather than just random skill in whatever he is casting at the moment.
