Currently, if you go to improve a suggested edit, you jump out of the review page, and it's awkward getting back. It's not impossible, just awkward, which makes you (well me, in any case) hesitate to bother to improve.
I haven't got any great suggestions or preferences. I guess in-line edit would be the best (as per this similar request for the other review tabs). Another alternative would be to have it open in a new tab - anything which doesn't result in having me navigate out of the review queue.
(In passing, one thing to look out for if it is inline is that you need to match the same width as the final post: because one of the things I like to edit for is to avoid horizontal scrollbars on code sections)