As other episodes before, it would again have benefitted from more time. The resolution in the end happened very quickly; Angel was about to ruin everything, but a simple "I'm sorry, I messed up" from Spike was enough to stop him, the Mane Six somehow never discovered all the critters under their seats, and after that everything just fell into place and after the moral of the story'd been driven home (without a letter to Princess Celestia this time), it was over already.
The lack of time was also evident elsewhere. The Cutie Mark Crusaders, for instance, were press-ganged into helping Spike very quickly, although Spike's playing into their desire to earn their cutie marks worked well. Later on, it seemed a little random when he just grabbed them from the bridge, although the visual gag with their goggles made that less obvious, and their desire to see the Crystal Empire provided a good reason for why they just went along with everything from then on.
Zecora was another instance. I felt that she, perhaps, could've played a much stronger, more pivotal role in this episode; she nailed it right away when she said that Spike's dragon greed was "bad mojo", but her appearance was ultimately of no consequence. Not just did Spike ignore her words of wisdom, the script itself also didn't build on her appearance any further, and it remained random.
I'm not complaining, though: I love Zecora, and I loved her here, and we got some beautiful views of her from all sorts of angles. :)
What else? It was interesting that gems are apparently a sort of currency in Equestria; I always thought that while they were admired for their beauty (hence e.g. Rarity using them for her designs), they weren't ultimately held to be of any real value (by the ponies — Spike at least finds them delicious, so they have a certain inherent value to him).
Speaking of Spike again, I liked the quick thinking he displayed with the "we thought we'd meet you at the station" bit in the end. Clever! Of course, he also already showed his quick wits when throwing the gem earlier — and speaking of which, the show really involves a lot of throwing, doesn't it? At least this time, it wasn't wives. :)
And all the pets were adorable, of course, even Aloysius (who was always one of my less favorite characters). Perhaps it's the neverending stream of "who?" jokes — I'm easily amused by such things. :)
Winona was adorable as always, of course, and I liked how she was portrayed as a real dog, pretty much, from her chasing critters to her howling along with Spike's "WHYYYYYY!" in the end, and from her fondness for belly-rubs to her eagerness to show affection. I also liked just how much fun she seemed to have with the industrial-sized pet hairdryer. *s*
Tank, Opal and Angel were about what you'd expect from them. So was Gummy, of course, and it was nice to see Pinkie interacting with him. BTW, did he have teeth now? I'm at a loss as to how you would floss toothless gums, at least.
I also liked the large number of cameos — I can recall at least Berry Punch, Colgate, Donut Joe and Carrot Top right off the top of my head, and I was also happy to see that Screw Loose apparently had one of her quieter, happier moments, although her existence still breaks my heart, and her "special talent" still makes me deeply uncomfortable. I suppose she's well-cared for, at least.
The episode also had a lot of ponies, didn't it? Between all these cameos (and more!), ALL the Mane Six, Spike, the CMC, Zecora, and ALL the pets, they really tried to put a lot of characters into this episode. Not that I'm complaining, mind you! :)
Another thing I liked: the Rainbow Dash poster and the Rainbow Dash balloon pony (!) in the CMC's club house. Scootaloo really looks up to her, doesn't she? :)
The ONE thing I didn't like about this episode was Spike bribing Granny Smith — or rather, her accepting the bribe. I don't think anypony should have done that, but Granny Smith of all ponies? She's old, she's wise, she deeply cares about doing "the right thing" (or so I think!), and she's related to the Element of Honesty of all ponies. So this definitely seemed out of character for her.
But outside of that? Great episode.