Abomination and Whiplash were pretty damn awesome, IMO. We have yet to see the actual Mandarin but IMO the twist with the Faux Mandarin was pretty damn clever and something that will not be soon forgotten.
Well, I was only referring to MCU villains. You start bring up Elektra amd Ghost Rider and AngHulk

and of course they all suck. Those were god awful movies and their villains reflected that. But those were made by FOX, Sony & Universal. IMO there are lots of poorly done villains in non-MCU Marvel films, most of them are that way in fact. It's just that among MCU villains I'd say Malekith got shafted more than any of the others. Whiplash & Abomination still got to have some great scenes. Malekith was relegated to speaking in a foreign language for most of the movie and it's hard to have a great scene with some memorable dialog when you're doing that. His end fight with Thor was cool but that was about it. Another reason was that he had to share villainy space with Kurse(who's barely a character at all).
I totally agree that it was a huge mistake having Malekith speak Elvish, that really robbed him of some potentially great lines - Chris Eccleston is a terrific actor, he was freakin' Dr Who for God's sake, but he really didn't get a good go in TDW. I know that in LOTR Peter Jackson manages to have the Elves speak their own language and sound cool - but that didn't really work here - it just sounded silly.
On the other hand I felt Kurse, post-transformation was a pretty legit villain, sort of a Dark-Elf Terminator. Yes, he was an evil henchman, but he did it well. He's menacing and clearly a serious threat to Thor and co, and comes across that way without a single word of dialogue. So I didn't have any problems with Kurse.
Did you really like Whiplash ? I mean I respect your opinion, but wow I found Mickey Rourke pretty hard to stomach in that role - but that's just me.
As for Abomination, as Emil Blonsky (Tim Roth) he was pretty good -but that's Tim Roth for you. I didn't find the post-gamma infusion version of him either scary or particularly interesting, he was just a slightly bigger Hulk with some bones sticking out.
Personally I couldn't call anything that either of them did "awesome" in those films, maybe 'average' at best. So, agree to disagree on that one.
But back to your original point, I do agree that Malektih had a lot of potential as a character, and was portrayed as a solid actor, but didn't really make a particularly memorable villain (sadly, I think we could say the same about Ultron).
And whatever you think of the plot twist with the Mandarin, he was never boring, and Ben Kingsley really brought his A-game in making the character memorable. I personally loved his scenes in IM3.
As for the Mandarin. Yes Ben Kingsley was great, but then it's hard to find a film where Ben Kingsley is **** - he's been in **** films, but he's pretty much always awesome, I don't think he has a B game or a C game.
However, I didn't like the interpretation of the character - I think there are some characters for whom a twist like that would have worked, but the Mandarin wasn't one of them.
That's just my opinion of course, and I know that opinions are divided on the decision to portray the character that way. Some loved it, others did not.