With the tempo comment, what I mean is that sudden tempo switches can throw people off guard. It takes time to ease into a new tempo, and I personally don't do many tempo changes because I think it's hard to make it work without raising eyebrows.
With timings, YMMV; with nonphysical instruments I don't mind as much, but with realistic instruments, stiff timing highlights how sampled they are, and even slightly random timing in either direction (a few ms) helps.
Besides what I mentioned, I don't have anything else to mention; maybe it doesn't seem like much, but I think it's enough to last you if you keep referring back to this list and seeing if any of these still are issues.