1. He is very caring.  If you are hurt, Hagrid will help.  An example is when they were walking back from Hogsmeade and Katie Bell kind-of went insane.  Harry ran to Hagrid for help.  Not Dumbledore, not Madam Pomfrey, Hagrid.

2. He is trustworthy.  The example for the first reason is also an example for this one.  Also Dumbledore trusts Hagrid to pick up the Sorceror's Stone, get Harry, and persuade the giants to come to Dumbledore's side.  And we just can't think that Dumbledore's bad!

3. He is loving.  He loves things most people won't love, like Grawp, Buckbeak, and thestrals!

4. Although big, he is polite.  Hagrid, like other half-giants might do, doesn't come bursting into houses and demanding something.  He is a normal person, except his height and weight.  Who cares about that kind of stuff!

5. Hagrid is kind.  He helps needy people.  He helped Harry a lot by telling him the truth about the wizarding world. If he were bad, he'd probably lie a bit about you-know-who and call him the Dark Lord.  Instead he told him the complete truth.