Sometimes, it's okay for a race to be really simple. Using 4e as an example, Humans were special because their features were powerful but simple: any single stat could get +2, you got a bonus feat (the
only race which had this), a bonus at-will attack (or Heroic Effort later), a bonus skill training with no restrictions (e.g. not just a class skill), and a small bonus to all non-AC defenses. Nothing fancy, but something
plenty of characters could leverage very well.
Turning to 5e, I think the default Dragonborn give us an excellent baseline for a not-quite-sufficient race. They've got exactly four things: +2 to one stat (Str) and +1 to another (Cha), Draconic as a bonus language, resistance to one chosen element, and a short-rest breath weapon. Thing is...that resistance is kinda bland and minimal as far as features go, and the breath weapon isn't much better.
Unfortunately, several other PHB races (dwarves, elves, and particularly half-elves) are rather
above the curve instead of below it, so the original default dragonborn really stick out like a sore thumb. It's part of why they were the first race to get a true "complete replacement" thing, 'cause they kinda needed it.
For my part, if Dragonborn had had (a) some additional, skill- or utility-focused feature, and (b) some additional hardiness- or regeneration-focused feature, I would have been perfectly happy. As an example:
Proud History. Dragonborn have a knack for remembering the great deeds of the past--whether as something to measure themselves against, or as lessons to be learned from. You have proficiency in the History skill, or Expertise if your class or background provides History proficiency.
Draconic Blood. In the heart of every dragonborn flows just a little of the resilience of true dragons. When you spend Hit Dice to recover HP as part of a short or long rest, you gain +1 HP for each hit die expended.
There. Relatively small things, just a tiny bit of extra HP and training (or expertise) in a skill that
might be useful...or might just be flavor, depending on the campaign.
And yes, the weight or impact of the feature matters. Variant Humans get only two distinct +1-to-a-stat, but they also get a bonus feat, something extremely valuable in 5e, and a bonus skill, something generally pretty nice to have (since
most characters never gain more than 4 skills total). Despite having
fewer (3 vs 4) and partially
weaker features than Dragonborn (+1/+1 instead of +2/+1), Variant Human is one of the strongest races in the game, because feats are THAT good.