iMessage not delivered as text!!!

When I text someone with Samsung (who recently switched from iPhone), he is not receiving my texts. When initially sent, it says iMessage, then switches to sent as text message. However, he doesn't receive all texts, just some, and doesn't receive group messages.

Not liking Apple these days...very frustrated. It should not send as iMessage if the phone is not an iPhone. I have deleted all texts, and changed his phone to mobile in my contacts.

C'mon Man!!!