Never were I ever a pro player in card games, however they've been accompanying me for a larger part of my life. Unfortunately some of those are discontinued or totally abandoned, but here is a list of games that I can remember right now that I've played:
- World of Warcraft TCG - most probably killed because Hearthstone was projected to be a big hit card game based in Azeroth. Didn't spend a lot of the time on it, only knew rules and had bunch of commons, played maybe 3 games, but I remember it fondly.
- Runescape: Chronicles - still somewhat active, it launched in the summer. It was really unbalanced, had few OP cards of SR rarity (diamonds), however it quickly becomes a monotone game. The construct of it is interesting though. Each game is composed in 5 chapters, each chapter has 4 card slots available. You can either fight monsters or use spells, which can also interact with the cards put by your opponent, it could lead to some mindgames and yomi layers, but you had to suspect the cards your opponent was running. It is still available to play, however the playerbase shrunk even more from the small one it initially had. Fun for couple of weeks, give it a try if you want new experiences.
- Duelyst - you didn't mention it, so I will. Haven't played too much since besides the graphics I didn't really like it that much. It is a board/figure game meets card game. You can summon on specific areas, you can boost or destroy other cards, your goal is to defeat enemy hero. Fairly big and popular, not as much as HS, but who isn't.
- Summoner Wars - it also has an online version to check out as far as I know, but mainly I know this from playing IRL. Fun game, also as the game mentioned above played on a field with cards. There are many races to play with, nearly each one of them can be "competitively" playable, the major drawback for me is that damage in its is RNG based, each card has a number of dice you are rolling when attacking and usually result 3+ is damage. For spectators it's certainly fun, however losing because of rolling five times a 1/2 while your opponent hits all the neccessary ones can be frustrating
And finally, RIP sweet prince
- Might and Magic - Duel of Champions: this card was my favorite card game until Base Set 2 happened. Setting aside Ubisoft trying actively and passively to kill it, until the try at the complete overhaul which incredibly slowed the game and made it not fun to play, there was few decks that could be dominant. Of course it had some OP stuff that nobody enjoyed playing against such as Kelthor or Prison, however through rose tinted "nostalgia" glasses it was still the best card game I've ever played. The main advantage of it it had near 0 RNG (except for card draws of course), interesting mechanic in the terms of field (each player had 2 columns with 4 rows, certain kinds of creatures could occupy either of the rows, spells could be affecting single targets, rows, columns or areas, so not only you had to place your cards in the best position for offensive, but also appropriate against the threats that your opponent could pose). Unfortunately after a while it became dead without visible support from Ubisoft, and then Bluebyte, then it was announced that it was finally getting an arena/draft mode promised long time before but simultanously stopped receiving any further patches/bugfixes and finally at the end of October of last year the servers were completely shut down. One could argue that HS overshadowed DoC, that it had no chance of big success as the numbers on Twitch on really great days and dev streams were reaching maybe 1k viewers, however it is still atrocious how Ubisoft treated this game and its community.
You already mentioned MtG and YGO, so I didn't write anything about them. For sure I'm forgetting some TCGs, if you look for more board game card oriented stuff, then I can recommend 7 Wonders or Dominion off the top of my head.
Also, I have no professional experience in this field, however TCG design is extremely difficult, to invent a system which is interesting and isn't a copy of already existing one is hard. Also TCG market is, at least in my opinion, rather closed with a hegemon being MtG irl and online/mobile HS, maybe Clash of Clans or other stuff like this. Take a look at the most successful card games outside of this trio and how many active players they get worldwide compared to the enormous ones. And then take a look how many are fresh ideas without an already established universe which can draw some new players. Suppose you have a nice new system, now you have to balance it and create a great number of cards which provide interesting gameplay choices, it would be also nice if there was no overpowered or underpowered stuff, and even if you have each of the element done, you still need to find a playerbase for it. There isn't really a conclusion or an idea in this paragraph, only my general thoughts on the subject.