I agree very strongly with the idea of Return to the Tome of Horros being vastly superior to Tome of Horror 2. So much so that I truly believe not continuing with that naming trend would result in a drop in revenue. i could easily be wrong, but that's how I feel.
I also agree with the earlier comment on strengthening the written descriptions of what these things are and do. Admittedly it wasn't much of problem for me, and there are those great pictures right there on the same page, but i did notice they were a tad, uh, not as effective as they could be.
And, really, why not hae some older converted monsters in there. It's not like your conversions are ever quite the same as their conversions. I like yours better. Maybe not as high a percentage as the last book but at least a few. As a fan service if nothing else.
p.s. I could have sworn someone already did a seemingly nice and proffesional conversion of most of the spelljammer bestiary somewhere out there on the net. I am wrong about that?