You love someone - you genuinely love them. They make you happy, they are a good person, they've been there for you, you know they'll always be there for you, but you feel no chemistry, no romance there.

In love with someone - you get the butterflies in your stomach when around them, you love everything about them, feel a lot of chemistry between them, there's a lot of romance.

I think the biggest difference is chemistry and doubts... When you're in love with someone you have no doubt of your relationship and where you wanna be, and you feel that chemistry. When you love someone but are not "in love" with them, you might not feel that chemistry, and you probably have a lot of doubts in the back of your head of your relationship and where it's going.

All my opinion, from my experiences.