I'll never know Zaeed or Kasumi.
Nor will I know the important to plot day one DLC character for ME3.
You aren't missing much. Zaeed has one of the most boring and stereotypical personalities ever, while Kasumi has some funny comments here and there, she's a bit too much of a Star Wars reject and only "so so" for usefulness. Zaeed is only ever useful if you aren't playing a character that has squad disruptor ammo for Geth missions and early for Jack's recruitment. Mordin usually has something interesting to say, and on top of that is one of the more overall useful characters in combat.
I also just don't get all of the Tali love. I mean sure, she was interesting in the first game, but Garrus and Wrex were much more interesting, and she has a pretty awesome loyalty quest, but that's about as far as it goes. Oh no, she's a displaced Israelite, must gush? As a teammate, she's always sucked. I know that helmet adds this huge air of mystique for the geek squad, but she doesn't look like a human supermodel underneath. She looks more like a Predator and Batarian had a kid. Just wait, you'll see...
Most interesting for their personality and backstory: Garrus, Mordin, Miranda, Wrex, Tali, Legion
Most useful squadmembers: Miranda (until she's dead), Mordin, Grunt, Garrus, Thane, Samara, Legion and Zaeed situationally
Most boring for their personality and backstory: Zaeed, Liara, Kaiden, Ashley, Kasumi, Jacob, Samara (the loyalty quest is cool, but super short and Samara's delivery sucks)
Worst Bioware character ever created: Jack; nothing more than a marketing tool that worked.
Haha, I just read John's post about the story Hamburgler was trying to write. Does that sound like Warehouse 13 to anyone else?