I guess Wrex doesn't play much more than a minor role in the future games, then. That's a shame because I really like him. I'd like to be able to find a way to cure the genophage. (No spoilers, please. I'm sure it's possible that there is such a mission and I just don't know about it.)
I won't spoil anything, but I will say that you most certainly haven't seen the last of Wrex.

When I was going through my squad screens I noticed there seemed to be slots for about 10 characters in ME2. That seems like a lot. At the risk of going a little off-topic here, I'm going to say that I prefer games where you either have a small team that stays consistent throughout the game (i.e. FF X-2), or multiple characters but you are forced to take certain parties for the majority of the game (FF IV, FF XIII). I never liked having the option to have tons of characters (like Chrono Chross) because it seems like you get into a groove with a certain party and then you never want to switch it up. Agree/disagree?
Without going into specifics, ME2's cast is very diverse and it's the kind of line up that has something for everyone. You'll very rarely hear anyone complain that that didn't like *any* of the squadmates.
Honestly I can appreciate both approaches. A larger pool of characters means you can change things up more often, but I think most people tend to pick their favourites early on and stick with them.
What I don't like is when they make some characters indispensable. For example, in DA2, unless you were a healer yourself you pretty much *had* to drag Anders around with you and likewise, unless you were a tank, you pretty much had to pick Avaline.
of course your own class is always going to dictate your choice to a certain extent, but it's nice to have at least two different options to choose from, especially when it comes to a vital role like healer or tank.
Of course the drawback of too much choice is that there's always at least one character that is such a "jack of all, master of none" you *never* use them past the first few missions. *cough* Jacob *cough*