Runequest
No character classes: everyone can fight, everyone gets magic, everyone worships a god (with a few exceptions), and your character gets better at stuff they do or stuff they get training in. The closest there is to a character class is the choice of god your character worships (which dictates which Rune spells your character might have) but there is plenty of leeway to play very different worshippers of the same god.
No levels: your character gets better at stuff they do or stuff they get training in. As they progress in their god's cult they also get access to more Rune spells.
Intuitive percentile 'roll under' system: an absolute newbie who's never played any RPG before can look at their character sheet and understand how good their character is at their skills: "I only have 15% in Sneak, but a 90% Sword skill - reckon I'm going in swinging!'"
Hit locations: fights are very deadly and wounds matter, "Oh dear, my left leg's come off!"
Passions and Runes: these help guide characterisation,and can also boost relevant skill rolls in a role-playing driven way, e.g invoking your Love Family passion to try and augment your shield skill while defending your mother from a marauding broo.
Meaningful religions: your character's choice of deity and cult provides direction, flavour, and appropriate magic. Especially cool when characters get beefy enough to start engaging in heroquesting - part ceremonial ritual, part literal recreation of some story from the god time.
No alignment: your character's behaviour can be modified by their passions, eg "Love family" or "Hate trolls", and possibly by the requirements of whatever god you worship, but otherwise is yours to play as you see fit in the moment without wondering if you're being sufficiently chaotic neutral.
Characters are embedded in their family, their culture, and the cult of the god they worship: the game encourages connections to home, kith, kin, and cult making them more meaningful in game and, in the process, giving additional background elements to take the edge off murder hoboism (though if that's what the group really wants then that's a path they can go down (see MGF, next)).
YGMV & MGF: Greg Stafford, who created Glorantha, the world in which Runequest is set, was fond of two sayings. The first is "Your Glorantha May Vary". If is a fundamental expectation, upheld by Chaosium, that while they publish the 'canonical' version of Glorantha any and every GM has the right to mess with it for the games they run. Find the existence of feathered humanoids with the heads, bills, and webbed feet of ducks to be too ridiculous for your game table? Then excise them from the game with Greg's blessing! The second is the only rule that trumps YGMV, and that is that the GM should always strive for "Maximum Game Fun".
While we're on the subject of Glorantha, the world of Glorantha! It's large and complex and very well developed in some areas (notably Dragon Pass and Prax) but with plenty of space for a GM to insert their own creations. It is, without doubt, one of the contenders for best RPG setting of all time.
To continue on the subject of Glorantha, there is insanely deep and satisfying lore if you want to go full nerdgasm on it. But you can play and enjoy the game with a sliver-thin veneer of knowledge: "I'm playing a warrior who worships Humakt, the uncompromising god of honour and Death." The RQ starter set contains everything you need to get a real taste for the game (ie minimal lore) and is great value for money since it's what Chaosium hope will draw people in.
Ducks: ducks are cool and not to be under-estimated.