I always look for things to occupy time! IE, games, dress ups, possible combinations of colors and species, an active forum, that sort of thing! I've also always liked premium currency, but not when it can be used to get so far ahead in developing your gameplay that every other one that starts out can't do anything properly
Flight Rising is a good example, since there isn't really a "Gem to Treasure" button, so you can't expand your lair immensely by just spending $20 or so
Most other adoptables games I've played seem to either not have premium or have a way to shift it from premium to generic, which never seemed fair to those of us without the money, patience, or time to get where others that have paid have gotten.
I will say that I dislike, and sorry Pixpet, not being able to customize a little more about your creatures. One of my favorite parts of (wow here's an old one) Neopets, of all things, was being able to buy clothing or smaller pets that traveled with it...!
Besides that having a pixel companion is always truly fun to me x3

Can I hoard things?

Obviously I have my priorities straight.

Is it unique? What’s unique about it if so?

Some sites have same-site-syndrome (a LOT of pokemon sites for example), so I like to look at sites and ask what can I do here that I can’t do on other sites?

Community, community, COMMUNITY!

A site can be great in terms of PLAYING it but if the userbase isn’t really friendly it’s a huge turnoff. I love interacting with a website’s community so what’s the point of sticking around if the community isn’t nice?

Friendly and helpful staff and owners

Similar to community. You want the staff to be friendly, helpful, and listen to its members. When this doesn’t happen and you encounter problems with the site or other members and the staff or owner doesn’t care or doesn’t reply it’s really annoying/bothersome

Edit:

Reading over what’s already been said I’ll respond - You can customize your pets here. Not in a Neopets way, but it’s more in a ‘make your own OC and be imaginative with them’. You can’t overlay your design like you can on Furvilla and Aywas, but it’s still a bit of charm. You can display the design in your signature and on your profile. It was like this on Komodo’s previous website and it works.

As for a PC to $$$, no you’re right there isn’t a button for that or an auto player exchange, but most sites don’t have that and I’ve only ever seen it on Sylestia with its currency exchange (people put up diamond in exchange for site currency or vice versa.) People CAN send PPT to other players though.

Mini games are always fun time occupiers and have been suggested here a multitude of times. Keep in mind this site is NEW and Komodo is one person and the only coder on the site. He can only do so much at a time. The demand for new features in comparison to a single Komodo doing the coding is a massive difference. He’s taking care of mechanics first things first.

>> When investigating a new pet site, what features do you look out for?

things to do! a variety of ways to earn money, and a vibrant community. oh, and cute art :)

>> Are there any specific mechanics/activities from one site that you really like?

dom battles on flight rising are one of my fave things, even though it's not really a site feature as much as a community made feature lol.

>> Is there anything you dislike?

drama websites, but that's a constant now :x

>> How do you feel about premium currency? Idealistically what content do you think it should encompass?

i'm okay with premium currency as long as it doesn't give an unfair advantage.

Needs to be things to keep me engaged. At least a goal to work towards, even if the actual activity of playing the game is simple and repetitive. The in-game mechanics need to be polished and fair, not gimmicky with high fail rates. I should not be punished for playing on a pet site, that makes me want to quit. Lioden, with its massive amount of engaging activities and different ways to play the game was by far the best pet site I've ever played.

Obviously I join sites about things that interest me, always about animals/creatures solely. I don't like making a human avatar, but Pokefarm Q I'll excuse (because it's Pokemon.) As I mentioned before, mechanics designed to punish you or are incredibly unfair are a no-go. I will not play your game.

Premium currency should be obtainable as Flight Rising and Lioden do it--as in, you're allowed to sell your items on player market boards for said premium currency. It's still hard to make, but not completely barred off from people who cannot pay for it. "Exclusive shops" for paying members only containing necessary or important items are the worst. There should be a way for all players to make a little bit of that money.