I enjoyed that game a lot when I first bought it, and I think I enjoyed it even more when I bought it after it was re-released on the eshop (in 2014?). It was far too short, in my opinion, but as someone who only ever really collected the original Pokemon cards (the base, jungle, and fossil sets), I enjoyed playing a game that featured the cards and rules I grew up with. At this point, I still play it a bit, but I've pretty much run out of things to do unless I try to max out my card count, which seems kind of pointless. I like making new decks sometimes, but my current one works so well that I hate switching it up.
I really wish they had released the second version in the US, but as far as I know, it only appeared in Japan (and never in English). It sounded more involved, and it would have been fun to return to the TCG universe. Maybe I'll try it sometime in the future, but for now, I'm stuck with the original.
TCG online doesn't really do it for me. Unlike with the main series games, I haven't kept up with the TCG (the cards were too expensive for what I felt like I got out of the packs, so I have a few newer cards, but not too many). As a result, I found the power creep and changes in the rules really jarring in TCG online, and while I'm sure I would get used to them, I just didn't get that into it. I think another problem, though, was that I tried playing it while in a hotel room, and my wifi kept giving out and kicking me out of the game. If it were released as a stand-alone 3DS title that did not require a constant internet connection, I would probably buy it, and likely enjoy it.
I would love to see a new TCG game, but I wish it could have a way to feature usable versions of all of the cards, new and old. Or at the very least, all of the Pokemon should be represented (I don't know if that's the case now or not, but as a Kadabra card hasn't been made in years due to lawsuits, and old sets cannot be used competitively after a certain length of time, I presume that not every Pokemon is available in the modern sets).