While Haeg may have some more gameplay mechanics, and this is coming from someone who only played the demo of Haegemonia, Haeg lacked a few subtle things that made Homeworld special well beyond the gameplay aspects.
The first thing being story and soul. Something about the extreme loneliness and emptiness of the Homeworld's visuals that were accentuated by the so pace made the game fell like you were looking at something timeless. Yet, it still hit you emotionally. Maybe it had something to with making you lonely so you grow attached to the few voices you hear.
Homeworld is one of the few space-based games that got motion right. In Haeg, ship movement and explosions felt canned and lacked fulidity. It's a subtle thing, but watch ships fly around in Haeg. The look like they're moving on strings or turning on dials. It's just doesn't feel as good as some of the games that really get it right like Homeworld. It's a problem a lot of games have and to me it's one of those details that are a small step that make a huge difference. Homeworld's also has a purposely sparse look that way more stylish from what I saw in Haeg and that's the sort of thing I can get behind. Haeg's looks were all about flashy textures and high resolution explosions and that's amaturish in a lot of ways. It's like what developers who rush to get games out for console lauch line-ups do. It takes great screenshots, it looks stiff and sloppy on the go.
Generally, what makes the Homeworlds special is more about the experience of the single player campaign. Honestly, I almost couldn't care less about the skirmish or MP of the games. It's easier and less memoriable to make a game that just plays well, but if you make a game that plays slightly less well but hits all the right notes in terms of impact it's gonna be with you a lot longer and takes a gentler touch. Like I said, I only played the demo of Haeg, but I felt little when I was playing it... it felt like I was playing a game. Homeworld makes me feel like I disappear. Besides, it's not like Homeworld's actual game is in any way lacking. There's more than enough meat to carry me through the campaign without all the other stuff. I'm also of the mind that some of that stuff added gameplay-wise muddled things up and were the sorts of things that are added just to make something "new."
In short, never compare anything to Homeworld... I'll cut you.