In a word, Dagger is Superb!
GET DAGGER if you have kids or even if you enjoy rules-light gaming as an adult. It uses any OSR game as a base, so you can use Descending or Ascending AC, whichever you like better. But even if you don't have your "big" books with you, You can play Dagger on the fly, so it may serve as a good, cheap, on the go pick up game or a simple game to introduce new players or to take camping. But to introduce kids to tabletop RPGs, it's perfect.
I think I'm becoming minimalist in my gaming preferences because Dagger has no Attributes and I find that liberating! That's right, no STR, DEX, CON etc... how is this possible? You know what? it totally works!
Dagger is designed to distill OSR/D&D down to the minimum to make it accessible for kids as young as 5. I dare say it does this flawlessly. This Sunday, I 'ran a combat' with my 5 year old daughter, and she basically got it on the first try. She just turned 5 in January and it was a hoot. I can totally see this working for kids 5-10. I can see how using figures would totally help with younger kids.
The spell list captures the iconic spells of the game, and the rule book states it's a suggested list. With only 4 spells of each level (levels 1-5) you may want to add more, and it's super easy to do (which was the bulk of my house rules). You can basically just plop in spells from from S&W, OSRIC, Labyrinth Lord, C&C, D&D Oe, 1e... not hard to fudge it on the fly even. That said, since this is for 5 to 10 year olds, keeping a tight focus (that is, short spell list) is wise. Also, with no Ability stats, spells like (Bull's) Strength and Haste simply won't work.
The characters are simple but effective at capturing the essence of each class, and here, as you may expect, Dwarf and Elf are classes. You can of course, call the Knight an Amazon or Warrior Princess or the Wizard a Fairy Princess or whatever any player wants, really. They can be a Gorn or zombie, even, and the rules support this on the fly make-believe fun; as they should!
So in brief, Dagger does what it sets out to do, and it does it well. It's great as an introduction to gaming for the young or for older kids or even grown ups who are afraid of dealing with a ton of rules.