Fanaelialae
Legend
I love the concept of the 3ed Savage Species, but I've problems with it's execution. Still trying to find the right balance between them.
The problem I had with execution was around one 3ed concept: HD+ECL - the insistence that every HD was equal to a class level I strongly disliked. First many of the monster types were significantly weaker than PC classes, it just didn't work out. Add in dead levels of ECL that did very little (not even increase max skill levels IIRC?) and it really handicapped you mechanically. Plus it made spellcasters basically impossible.
Actually, I'd love a system that started around level -2 or -3. All races have racial classes of varying lengths, with the "standard" race having 1st level as early teen, 2nd level as full adult and 3rd level as a "paragon". Plus a bunch of "background" 2 level long classes like urchin, nomad, high society, arcane school, soldier, and so forth. So you built your character with 3 levels taking at least 1 race and 1 background, and then level 1 is your first level of adventuring. Once everyone has racial levels fitting in races all over the place and not balanced against each other - just balanced at any particular level - becomes easy. A teen can age up to an adult by taking the second racial level, and any adult can take that single "paragon" level if you want to be even more elfy or whatever.
An example, you could have a human teen / urchin / acolyte. Or an dwarven adult / soldier. Or an elven teen / arcane school 2.
I agree about the issues in Savage Species.
I avoided them as best I could by creating a CR to level equivalency chart, then reverse engineering the monsters into classes. Thus far, I think I have yet to see one that has less hit dice than racial levels (the opposite is frequently true, but I haven't found lots of hp to be much of an issue in 5e). I haven't managed to get around the spellcaster problem significantly, though I have ruled that you can count 1/4 of your non-casting class levels towards your caster level for purposes of multiclassing (the idea is that even non-casters of high level have more "mana" than an average joe).
Admittedly, my data is limited as I've only had a few monstrous characters played to date (a harpy paladin, a hill giant, an awakened jaguar, and a mind flayer) but each worked fairly well, and didn't significantly over or under perform compared to the more traditional characters. I don't know if that speaks more to the flexibility of 5e or my system working as intended, but either way I'll take it.
Having various levels in race and/or backgrounds is a pretty interesting idea. Still, I'm not sure that there needs to be a level distinction between a teenager and an adult (otherwise, if you have significant downtime in the campaign, the DM might be forced to award a free level to any non-adults). I like the idea of racial paragons though. The backgrounds idea reminds me a bit of how Warhammer Fantasy Roleplay handles it's "classes". You could probably implement something like this in 5e (with a bit of work) by starting at a higher level. Otherwise, you're probably looking at something more like 4e with it's robust 1st level characters (which I personally liked a lot).