It's unusual, it seems to me, to have a theme which applies to every single clue, either in the clue or in the solution, or both.
I put two clues in right away, but then ground to a halt for a while, so I thought it looked like a difficult puzzle ... then suddenly I got going, and found it an easy one.
On the whole I liked it, but there were a few clues which I thought weren't very good. I agree with Chrise & Geeker about the "rather loose" definition of 24a. I thought the clue for 21a was insultingly easy: not at all the standard I expect in the Guardian. 1d was made too easy by having "lab" actually in the clue.
OK, having had my moan about what I thought were poor clues, at the other end of the spectrum, like several other people who have commentated, I liked 8d, and without a date that's my COD.
Jono suggests it might not be reasonable to expect us to know one aspect of 13a. Assuming Jono means the aspect that I'm thinking of, I didn't know it either, but I think the name is enough of a clue to suggest that it's likely, so I'm happy with that aspect of the clue.
Like others, I pursued a wrong answer to 23a for a while, but the correct answer is better than the wrong one, because the latter isn't primarily animated. The thing which did most to keep me off the right answer for longest was the fact that I didn't know it was a beagle.