STEP ASIDE EVERYONE THIS IS MY AREA.
Yaay! Another new Jdrama fan!
Honestly, I love Jdramas and live actions just as much as (even more really) than anime. I absolutely love jdramas and live actions - even though as you said, a lot of people have a terrible impression of them. I think it's mostly because a lot of people have seen the original anime/ read the manga and are iffy when things go exactly the way it does in the original source. Half the reason I tend to watch the live action before I watch the anime/read the manga - in most cases I watch/read them reverse Live action -> anime -> manga (unless it's new an airing)
I definitely have seen all of the ones you have mentioned and I can definitely recommend you a few you might like.
Paradise Kiss, Kimi ni Todoke and Hana Yori Dango, Yamada Taro Monogatari, BECK, GANTZ + GANTZ Perfect Answer and have recently started the Gokusen series.
Definitely watch them if they're 11-13 episode dramas since they pace quite well in comparison to movies, but that doesn't mean there are also some good movies there.
Since you have lots of romance/ high school base ones:
If you liked Hana Yori Dango, definitely try
Hana Kimi/ Hanazakari no Kimitachi. Legit haven't cried in any anime except 2-3 sports ones, and I bawled my eyes out at the end because it was finishingand was just really good. There's two versions 2007 and 2011, but most people prefer 2007. 2011 isn't bad, just the cast isn't as great as the original. Definitely has a lot of parts different from the manga, but didn't bother me much in the drama and I ended up liking it more.
THE GIRL WHO LEAPT THROUGH TIME/ TIME TRAVELER - This is soooooooooo so good. I did really like the anime, but I ended up liking this one soooooo muh more I cried with the unexpected ending. It's set with different characters and a different plot to the anime, but it carries the same theme of time travel. I recommend it to a friend who absolutely hated the original anime, but she ended up loving this. Definitely recommend it to anyone.
Yamada kun to 7 nin no Majo for if you want a supernatural + romance sort of thing/ I still prefer the drama way over the anime and It's pretty short for 8 episodes which is unusual, but it does the plot really well.
Kyou, Koi wo Hajimemasu I really liked as a simple movie if you want some "Shy teenage girl meets the most popular boy of school" and they fall in love. Apparently manga fans didn't like it, but a lot of the drama community who haven't read it really did love it.
For you loving GANTZ:
Mirai Nikki: Another World - I absolutely loved so much more than the anime/manga. Like The Girl Who Leapt Through Time, it's a different cast and story to the original, but same concept of cellphone death games. It was a little hard to begin with since I was used to the characters from the anime, but the live has it's own twist and is somewhat more ... realistic...(?) I guess than the anime.
Parasyte - So I haven't watched it's live yet since I'm waiting for both movies to be out (it's only just come out with subs). Apparently the movies absolutely ruins want you've watched if you have seen the anime/manga, but is brilliant if you are watching it for the movie alone without any knowledge. So don't watch it if you've seen the original source.
Maou - it's not based of an anime/manga, but if you like the other ones above, this is a brilliant drama you should definitely watch!
Other really cool adaptation in general, Asuko March!, Bambino!, Kindaichi series + movies, Tantei Gakuen Q movie + series.
Can't really think of anymore at the top of my head, but once I remember I'll probably post again or something.