I've had Pokémon Trading Card Game Online on my laptop for years, but aside from a few matches at the beginning I hadn't really spent much time with it aside from signing in occasionally to redeem the freebie codes that are given out periodically if you subscribe to the Pokemon emails. My nephew had gotten really into the physical cards and I'd played quite a bit of the Game Boy game, but it didn't seem substantially different than Yu-Gi-Oh, the only other TCG game I've really played.
It was only the threat of the game being shut down in order to make way for its replacement, Pokémon TCG Live, that I was kicked into gear and gave the game a closer look. It's been a while now that I've been much less into building my own decks and content on relying on theme decks, and the game has a daily challenge (e.g. knock out opponent's Pokemon with a fire type), a player levelling up system, and a vs. CPU mode that offers increasing levels of challenge, and those provided me with some motivation to play beyond just one or two matches. In addition, you're free to use any of the available theme decks, and those too feature a levelling up system where you have to win a certain number of matches in order to unlock all the cards in the deck. Of course, you can also play against real people, and there are one-off matches and on-the-fly tournaments you can join.
In terms of the game's mechanics, there weren't a whole of surprises for me since I stuck mostly to vanilla theme decks, but I think subsequent series and expansions introduce additional mechanics inspired by the video games. The game's interface works extremely well, and it's easy to keep track of everything that's going on, on your side of the board or your opponent's. It's fun to see the arwork and Pokemon characters on the cards themselves, although strategizing with the type advantages (which are a bit simplified compared to the video games as some types are consolidated together) seems a bit difficult given the big disadvantage the person with the type disadvantage has. I'm guessing there's some way that real life tournaments negotiate this deck selection process. Anyway, overall this was an entertaining enough diversion, although not hugely memorable. It turns out I have a bit more time to play this game if I want, as its successor has been delayed to next year. I don't expect that game to draw me in more than this has, but I'm sure I'll be checking it out at some point anyway.